Rename .js.erb files .js

Since we switched to more I18n-JS and JsRoute functions with f5739a33 and 2f03061f, we don't have the need to use a template engine for those files any longer.

app/assets/javascripts/markdown_ace_editor.js

@@ -14,4 +14,4 @@
         session.setUseWrapMode(true);
         session.setValue($(selector).val());
     };
-})();
+})();