Remove MatrixRTC legacy mode

This is the mode in which we sent membership events with the 'oldest membership' transport selection algorithm, which stopped being the default back in version 0.21.0. Users will no longer be able to select this mode in developer settings, and admins will no longer be able to select legacy mode through the config either. The app will still continue to support *receiving* membership events with the 'oldest membership' transport selection algorithm from others, however.

src/settings/__snapshots__/DeveloperSettingsTab.test.tsx.snap

@@ -285,50 +285,10 @@ exports[`DeveloperSettingsTab > renders and matches snapshot 1`] = `
           class="_container_1ug7n_10"
         >
           <input
-            aria-describedby="radix-_r_a_ radix-_r_c_ radix-_r_e_"
-            class="_input_1ug7n_18"
-            id="radix-_r_9_"
-            name="_r_0_"
-            title=""
-            type="radio"
-            value="legacy"
-          />
-          <div
-            class="_ui_1ug7n_19"
-          />
-        </div>
-      </div>
-      <div
-        class="_inline-field-body_1o4d9_39"
-      >
-        <label
-          class="_label_1o4d9_60"
-          for="radix-_r_9_"
-        >
-          Legacy: state events & oldest membership SFU
-        </label>
-        <span
-          class="_message_1o4d9_86 _help-message_1o4d9_92"
-          id="radix-_r_a_"
-        >
-          Compatible with old versions of EC that do not support multi SFU
-        </span>
-      </div>
-    </div>
-    <div
-      class="_inline-field_1o4d9_33"
-    >
-      <div
-        class="_inline-field-control_1o4d9_45"
-      >
-        <div
-          class="_container_1ug7n_10"
-        >
-          <input
-            aria-describedby="radix-_r_a_ radix-_r_c_ radix-_r_e_"
+            aria-describedby="radix-_r_a_ radix-_r_c_"
             checked=""
             class="_input_1ug7n_18"
-            id="radix-_r_b_"
+            id="radix-_r_9_"
             name="_r_0_"
             title=""
             type="radio"
@@ -344,13 +304,13 @@ exports[`DeveloperSettingsTab > renders and matches snapshot 1`] = `
       >
         <label
           class="_label_1o4d9_60"
-          for="radix-_r_b_"
+          for="radix-_r_9_"
         >
           Compatibility: state events & multi SFU
         </label>
         <span
           class="_message_1o4d9_86 _help-message_1o4d9_92"
-          id="radix-_r_c_"
+          id="radix-_r_a_"
         >
           Compatible with homeservers that do not support sticky events (but all other EC clients are v0.17.0 or later)
         </span>
@@ -366,9 +326,9 @@ exports[`DeveloperSettingsTab > renders and matches snapshot 1`] = `
           class="_container_1ug7n_10"
         >
           <input
-            aria-describedby="radix-_r_a_ radix-_r_c_ radix-_r_e_"
+            aria-describedby="radix-_r_a_ radix-_r_c_"
             class="_input_1ug7n_18"
-            id="radix-_r_d_"
+            id="radix-_r_b_"
             name="_r_0_"
             title=""
             type="radio"
@@ -384,13 +344,13 @@ exports[`DeveloperSettingsTab > renders and matches snapshot 1`] = `
       >
         <label
           class="_label_1o4d9_60"
-          for="radix-_r_d_"
+          for="radix-_r_b_"
         >
           Matrix 2.0: sticky events & multi SFU
         </label>
         <span
           class="_message_1o4d9_86 _help-message_1o4d9_92"
-          id="radix-_r_e_"
+          id="radix-_r_c_"
         >
           Compatible only with homservers supporting sticky events and all EC clients v0.17.0 or later
         </span>
@@ -491,7 +451,7 @@ exports[`DeveloperSettingsTab > renders and matches snapshot 1`] = `
       class="_field_1bd8c0 _checkboxField_1bd8c0"
     >
       <input
-        aria-describedby="_r_k_"
+        aria-describedby="_r_i_"
         id="cameraToggle"
         type="checkbox"
       />
@@ -521,7 +481,7 @@ exports[`DeveloperSettingsTab > renders and matches snapshot 1`] = `
       </label>
       <p
         class="_description_1bd8c0"
-        id="_r_k_"
+        id="_r_i_"
       >
         Configure resolution, framerate, bitrate, and codec for camera video. Changes apply on next call join.
       </p>
@@ -543,7 +503,7 @@ exports[`DeveloperSettingsTab > renders and matches snapshot 1`] = `
       class="_field_1bd8c0 _checkboxField_1bd8c0"
     >
       <input
-        aria-describedby="_r_l_"
+        aria-describedby="_r_j_"
         id="screenShareToggle"
         type="checkbox"
       />
@@ -573,7 +533,7 @@ exports[`DeveloperSettingsTab > renders and matches snapshot 1`] = `
       </label>
       <p
         class="_description_1bd8c0"
-        id="_r_l_"
+        id="_r_j_"
       >
         Configure resolution, framerate, bitrate, and codec for screen sharing
       </p>
@@ -598,7 +558,7 @@ exports[`DeveloperSettingsTab > renders and matches snapshot 1`] = `
       class="_field_1bd8c0 _checkboxField_1bd8c0"
     >
       <input
-        aria-describedby="_r_m_"
+        aria-describedby="_r_k_"
         checked=""
         id="echoCancellation"
         type="checkbox"
@@ -636,7 +596,7 @@ exports[`DeveloperSettingsTab > renders and matches snapshot 1`] = `
       class="_field_1bd8c0 _checkboxField_1bd8c0"
     >
       <input
-        aria-describedby="_r_n_"
+        aria-describedby="_r_l_"
         checked=""
         id="noiseSuppression"
         type="checkbox"
@@ -674,7 +634,7 @@ exports[`DeveloperSettingsTab > renders and matches snapshot 1`] = `
       class="_field_1bd8c0 _checkboxField_1bd8c0"
     >
       <input
-        aria-describedby="_r_o_"
+        aria-describedby="_r_m_"
         checked=""
         id="autoGainControl"
         type="checkbox"