Fix SCSS linting issues (#2207)

* Disable font-family-no-missing-generic-family-keyword for font-awesome accessibility icons

* Run stylelint --fix

* Avoid `@extend` directives with doodle modal CSS

* Drop use of `@extend` for notification cleanup buttons SCSS

* Run prettier on SCSS

app/javascript/styles/mastodon/tables.scss

@@ -361,7 +361,7 @@ a.table-action-link {
     }
   }
 
-  @media screen and (max-width: 870px) {
+  @media screen and (width <= 870px) {
     .accounts-table tbody td.optional {
       display: none;
     }