Update to use UserManager.getUserSwitchability()

Updated framework to handle user switchability cases, so use that
instead of CarUserManagerHelper.

Bug: 131776619
Test: Manually play with user picker.
Test: [1] Open User Picker
[2] Verify can switch to a different user user
[3] adb root && adb shell pm set-user-restriction --user 10 no_user_switch 1
[4] Verify can't switch to a different user
[5] adb root && adb shell pm set-user-restriction --user 10 no_user_switch 0
[6] adb root && adb shell pm set-user-restriction --user 0 no_user_switch 1
[7] Verify can user switch

Change-Id: Ie898723bd93a85d0ea01a9d0879af0c84e904c98