Revert "fix(button): incorrect text color when no color is passed in on dark theme" (#9555)

This reverts commit cd2b6df.

Author: jelbourn

src/lib/button/_button-theme.scss

@@ -77,7 +77,6 @@
 
   .mat-button, .mat-icon-button {
     background: transparent;
-    color: mat-color($foreground, text);
 
     @include _mat-button-focus-color($theme);
     @include _mat-button-theme-color($theme, 'color');