Remove stopgap color variables from previous design system

They have been largely unused for a long time. This changes the colors of checkboxes and the 'end call' button to align with current designs as well.

src/button/Button.module.css

@@ -5,10 +5,6 @@ SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial
 Please see LICENSE in the repository root for full details.
 */
 
-.endCall > svg {
-  color: var(--stopgap-color-on-solid-accent);
-}
-
 .rotate > svg {
   animation: spin 1s linear infinite;
 }

src/index.css

@@ -28,12 +28,6 @@ layer(compound);
   --font-size-title: calc(24px * var(--font-scale));
   --font-size-headline: calc(32px * var(--font-scale));
 
-  /* These colors are needed during the transitionary period between the old and
-  new Compound design systems, but should be removed ASAP */
-  --stopgap-color-on-solid-accent: var(--cpd-color-bg-canvas-default);
-  --stopgap-background-85: rgba(255, 255, 255, 0.85);
-  --stopgap-bgColor3: #444;
-
   --cpd-color-border-accent: var(--cpd-color-green-800);
   /* The distance to inset non-full-width content from the edge of the window
   along the inline axis. This ramps up from 16px for typical mobile windows, to

src/input/Input.module.css

@@ -173,14 +173,6 @@ Please see LICENSE in the repository root for full details.
   border-color: var(--cpd-color-border-disabled);
 }
 
-.checkbox svg {
-  display: none;
-}
-
-.checkbox svg * {
-  stroke: var(--stopgap-color-on-solid-accent);
-}
-
 .checkboxField input[type="checkbox"]:checked + label > .checkbox {
   background: var(--cpd-color-text-action-accent);
   border-color: var(--cpd-color-text-action-accent);