UX: Remove redundant focus style (#12192)

This style is unnecessary because text inputs and textareas have
focus styles set elsewhere (lines 228 and 288 respectively) and we don't
have any `select` elements.

app/assets/stylesheets/common/base/discourse.scss

@@ -186,10 +186,6 @@ textarea {
     border-color: var(--primary-low);
   }
 
-  &:not([type="checkbox"]):not([type="radio"]):focus {
-    @include default-focus;
-  }
-
   &:focus:required:invalid {
     color: var(--danger);
     border-color: var(--danger);