Opening Multiuser doesn't toggle it on

This does the following:
Simply opening Settings > Multiuser no longer
globally enables multiuser. The user would have
to actively toggle that switch to globally
enabled it.

(This reverts ag/7002640; a different solution for
that cl's bug is in the same topic as this cl.)

Bug: 137943217
Bug: 141372193
Bug: 149973281
Bug: 130270878

Test: manual: Settings > Multiuser doesn't turn on the systemui avatar
Test: manual: adb shell pm create-user A, does turn on sysui avatar

Change-Id: Ibfdd1dee408c7214d0a097c8d814dae87ffa82ac