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/_badge.scss

@@ -1,17 +0,0 @@
-@mixin badge-variant($bg) {
-  color: color-yiq($bg);
-  background-color: $bg;
-
-  @at-root a#{&} {
-    @include hover-focus {
-      color: color-yiq($bg);
-      background-color: darken($bg, 10%);
-    }
-
-    &:focus,
-    &.focus {
-      outline: 0;
-      box-shadow: 0 0 0 $badge-focus-width rgba($bg, .5);
-    }
-  }
-}