drop the now unused -color variable

Author: mdo

scss/_variables.scss

@@ -646,7 +646,6 @@ $popover-arrow-outer-color:           fade-in($popover-border-color, .05) !defau
 
 // Badges
 
-$badge-color:                 $white !default;
 $badge-font-size:             75% !default;
 $badge-font-weight:           $font-weight-bold !default;
 $badge-padding-y:             .25em !default;