Fix audio player controls color in mastodon-light theme (#14338)

Fixes #14337

The new audio player sets the background and foreground colors automatically
based on the thumbnail of the audio file, but the mastodon-light theme
overrides the controls' colors with a hardcoded color, which sometimes make
them unreadable.

app/javascript/styles/mastodon-light/diff.scss

@@ -767,10 +767,3 @@ html {
 .compose-form .compose-form__warning {
   box-shadow: none;
 }
-
-.audio-player .video-player__controls button,
-.audio-player .video-player__time-sep,
-.audio-player .video-player__time-current,
-.audio-player .video-player__time-total {
-  color: $primary-text-color;
-}