Remove the fallback AddSupervisedUserActivity.

Rollback the changes done in ag/16388725 and ag/16709333

Bug: 209659998
Test: croot && make RunSettingsRoboTests -j40 ROBOTEST_FILTER="com.android.settings.users.UserSettingsTest"

Change-Id: I75b85df50a3caff55375ad261a97225377644a38
(cherry picked from commit 86f350043905987fe950e1c197e1b27a8d9b73e5)
Fixes: 249057848
5 files changed