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/state/CallViewModelWidget.test.ts

@@ -35,11 +35,7 @@ vi.mock("../widget", () => ({
   },
 }));
 
-it.each([
-  [MatrixRTCMode.Legacy],
-  [MatrixRTCMode.Compatibility],
-  [MatrixRTCMode.Matrix_2_0],
-])(
+it.each([[MatrixRTCMode.Compatibility], [MatrixRTCMode.Matrix_2_0]])(
   "expect leave when ElementWidgetActions.HangupCall is called (%s mode)",
   async (mode) => {
     const pr = Promise.withResolvers<string>();