chore: remove SCSS code for :focus-visible polyfill

.changeset/forty-months-dress.md

@@ -0,0 +1,8 @@
+---
+"@utrecht/focus-ring-css": major
+---
+
+Remove the SCSS variable `$utrecht-focus-visible-fallback` and remove the following mixins:
+
+- `utrecht-focus-ring-reset`
+- `utrecht-focus-pseudo-classes-backwards-compatible`

components/focus-ring/src/_mixin.scss

@@ -4,8 +4,6 @@
  * Copyright (c) 2021 Robbert Broersma
  */
 
-$utrecht-focus-visible-fallback: true !default;
-
 @mixin utrecht-focus-ring {
   /* - The browser default focus ring should apply when these CSS custom properties are not set.
    * - Make the `box-shadow` value available, so components that have their own `box-shadow`
@@ -21,12 +19,6 @@ $utrecht-focus-visible-fallback: true !default;
   outline-width: var(--utrecht-focus-outline-width, revert);
 }
 
-@mixin utrecht-focus-ring-reset {
-  /* undo focus ring */
-  box-shadow: none;
-  outline-style: revert;
-}
-
 /* stylelint-disable-next-line block-no-empty */
 @mixin utrecht-focus {
 }
@@ -43,14 +35,3 @@ $utrecht-focus-visible-fallback: true !default;
     @include utrecht-focus-visible;
   }
 }
-
-// When support is needed for Safari versions that do not support :focus-visible,
-// use this mixin instead of the `utrecht-focus-pseudo-classes` mixin.
-@mixin utrecht-focus-pseudo-classes-backwards-compatible {
-  &:focus {
-    @include utrecht-focus-ring;
-  }
-  &:focus:not(:focus-visible) {
-    @include utrecht-focus-ring-reset;
-  }
-}