MDL-76842 auth_lti: don't update the user after membership creation

This isn't required and generates excess events. The only thing update
does, other than update the user fields, is to update the picture, but
in this case, that's unset in membership-based auths anyway, so it's
entirely safe to remove this.

auth/lti/auth.php

@@ -199,7 +199,6 @@ class auth_plugin_lti extends \auth_plugin_base {
                 }
             }
             $user = $this->create_new_account($member, $iss);
-            $this->update_user_account($user, $member, $iss);
             return \core_user::get_user($user->id);
         }
     }