Fixes results count in accessible text

Only counts the selectable items in the list. (filter out selected item)

Author: KayLeung

select2.js

@@ -1714,7 +1714,7 @@ the specific language governing permissions and limitations under the Apache Lic
                     self.liveRegion.text(results.text());
                 }
                 else {
-                    self.liveRegion.text(self.opts.formatMatches(results.find('.select2-result-selectable').length));
+                    self.liveRegion.text(self.opts.formatMatches(results.find('.select2-result-selectable:not(".select2-selected")').length));
                 }
             }