v5: Update badges (#28458)

- Drop hover and focus states
- Drop .badge-* variants and associated mixin for .bg-* utilities
- Drop .badge-pill for .rounded-pill utliity and adjust horizontal padding to find middle ground of .badge and old .badge-pill
- Remove unused variables
- Add default color value to .badge base class
- Update docs to reflect changes

scss/_mixins.scss

@@ -12,7 +12,6 @@
 @import "mixins/breakpoints";
 @import "mixins/hover";
 @import "mixins/image";
-@import "mixins/badge";
 @import "mixins/resize";
 @import "mixins/screen-reader";
 @import "mixins/reset-text";