Fixed height of group share dropdown

Closes https://gitlab.com/gitlab-org/gitlab-ee/issues/3149

app/assets/javascripts/groups_select.js

@@ -111,8 +111,7 @@ window.GroupsSelect = (function() {
   };
 
   GroupsSelect.prototype.forceOverflow = function (e) {
-    const itemHeight = this.dropdown.querySelector('.select2-result:first-child').clientHeight;
-    this.dropdown.style.height = `${Math.floor(this.dropdown.scrollHeight - (itemHeight * 0.9))}px`;
+    this.dropdown.style.height = `${Math.floor(this.dropdown.scrollHeight)}px`;
   };
 
   GroupsSelect.PER_PAGE = 20;