Fix focus styles in admin form controls

We lost focus styles on certain controls in commit 4dad04ae3, since we
were applying a border with a rule which had more precedence than the
rule of border on focus.

app/assets/stylesheets/layout/locale_switcher.scss

@@ -39,6 +39,7 @@
       width: auto;
 
       &:focus {
+        border: 0;
         outline: $outline-focus;
       }