Bouncer updates

Part one of many, to add a multi-user switcher to the bouncer for
supported displays.

This CL:

1. Removes a config that was not-needed, in favor of the
can_use_one_handed_bouncer resource.
2. Adds a new boolean resource to determine when to use the new
bouncer layout with user switcher

Test: atest KeyguardHostViewControllerTest
KeyguardSecurityContainerControllerTest
Bug: 206825213

Change-Id: I18e5e8ef68a57c5c633664062bb2f4fd5d7b778f