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
5 files changed