reorder simple form ul to list vertically (fixes #8236) (#8322)

* reorder simple form ul to list vertically (fixes #8236)

* remove browser specific prefixes

app/javascript/styles/mastodon/forms.scss

@@ -154,9 +154,8 @@ code {
       margin-bottom: 15px;
     }
 
-    li {
-      float: left;
-      width: 50%;
+    ul {
+      columns: 2;
     }
   }