Drop all hover mixins

Previously deprecated in v4.x, this clears out the now unused Sass option and removes some unused mixins. Arguably we could remove more, but I like the hover-focus mixin and we make extensive use of it across the project.

scss/mixins/_table-row.scss

@@ -26,7 +26,7 @@
     $hover-background: darken($background, 5%);
 
     .table-#{$state} {
-      @include hover {
+      &:hover {
         background-color: $hover-background;
 
         > td,