fix(material/progress-bar): remove track color workaround (#28416)

Previously we couldn't get the `track-color` to work through tokens, because it was generating an inline SVG. That's no longer the case so we can remove the workaround which also fixes the progress bar under M3.

Author: crisbeto

src/material/progress-bar/_progress-bar-theme.scss

@@ -18,21 +18,8 @@
 }
 
 @mixin _palette-styles($theme, $palette-name) {
-  $color-tokens: tokens-mdc-linear-progress.get-color-tokens($theme, $palette-name);
-
-  // We can't set the `track-color` using `theme`, because it isn't possible for it to use a CSS
-  // variable since MDC's buffer animation works by constructing an SVG string from this color.
-  // We also can't set the `track-color` by creating our own token slot because the track-color
-  // is set in the SVG string in `theme-styles`.
-  @include mdc-linear-progress-theme.theme-styles((
-    // TODO(crisbeto): the buffer color should come from somewhere in MDC, however at the time of
-    // writing, their buffer color is hardcoded to #e6e6e6 which both doesn't account for theming
-    // and doesn't match the Material design spec. For now we approximate the buffer background by
-    // applying an opacity to the color of the bar.
-    track-color: map.get($color-tokens, track-color),
-  ));
-
-  @include mdc-linear-progress-theme.theme($color-tokens);
+  @include mdc-linear-progress-theme.theme(
+    tokens-mdc-linear-progress.get-color-tokens($theme, $palette-name));
 }
 
 @mixin color($theme) {

src/material/progress-bar/progress-bar.scss

@@ -1,22 +1,14 @@
-@use 'sass:map';
 @use '@material/theme/custom-properties' as mdc-custom-properties;
 @use '@material/linear-progress/linear-progress' as mdc-linear-progress;
 @use '@material/linear-progress/linear-progress-theme' as mdc-linear-progress-theme;
 @use '../core/tokens/m2/mdc/linear-progress' as m2-mdc-linear-progress;
 
 @include mdc-custom-properties.configure($emit-fallback-values: false, $emit-fallback-vars: false) {
-  $mdc-progress-bar-token-slots: m2-mdc-linear-progress.get-token-slots();
-
   // Add the MDC progress-bar static styles.
   @include mdc-linear-progress.static-styles();
 
   // Add the official slots for the MDC progress-bar.
-  @include mdc-linear-progress-theme.theme-styles(
-      map.merge($mdc-progress-bar-token-slots, (
-      // Excluded because it is meant to be set by theme (b/273562256).
-      track-color: null,
-    ))
-  );
+  @include mdc-linear-progress-theme.theme-styles(m2-mdc-linear-progress.get-token-slots());
 }
 
 .mat-mdc-progress-bar {