Remove negative selector for `.select2-selected`

This broke scroll behaviour when displaying the selected items in the
dropdown.

select2.js

@@ -1402,7 +1402,7 @@ the specific language governing permissions and limitations under the Apache Lic
 
         // abstract
         findHighlightableChoices: function() {
-            return this.results.find(".select2-result-selectable:not(.select2-selected):not(.select2-disabled)");
+            return this.results.find(".select2-result-selectable:not(.select2-disabled)");
         },
 
         // abstract