mod actions: hide ip bans from non-mods.

Hide IP ban creation and deletion actions from non-mods in the
/mod_actions listing.

The previous approach of just filtering out the IP from the description
was hacky and didn't work with the `only` param (/mod_actions.json?only=id
still included the description field).

app/views/mod_actions/index.html.erb

@@ -20,7 +20,7 @@
             </td>
             <td class="col-expand">
               <div class="prose">
-                <%= format_text(mod_action.filtered_description) %>
+                <%= format_text(mod_action.description) %>
               </div>
             </td>
             <td>