Turns off use of refactord UserSwitcherController.

There was an automatically detected massive regression in performance,
as seen in the attached bug. This flag change shuts down the use of
UserInteractor instead of the controller.

Now, we have time to locally investigate the performance regression
before turning that on again.

Fix: 253435919
Test: verified that user switcher is still working
Change-Id: I716439dcbe55e998687229ab0e68176548eff685