Bug 1823783: remote username in user edit screen - adding back missing code

need to populate js variable that contains external auth instances

this code was removed in following patch but we need it
https://reviews.mahara.org/#/c/8528/21

behatnotneeded

Change-Id: I7789cd3f61738de775df73c6eb5f1bc7a7f039be
(cherry picked from commit 03b8a0a6)

htdocs/admin/users/edit.php

@@ -204,6 +204,11 @@ foreach ($authinstances as $authinstance) {
     foreach ($user_insts as $inst) {
         if ($authinstance->name == $inst->institution || $authinstance->name == 'mahara') {
             $options[$authinstance->id] = $authinstance->displayname . ': ' . $authinstance->instancename;
+            $authobj = AuthFactory::create($authinstance->id);
+            if ($authobj->needs_remote_username()) {
+                $externalauthjs[] = $authinstance->id;
+                $external = true;
+            }
         }
     }
 }