Migrate KeyguardClockSwitch to new shared Clock library

This change modifies the KeyguardClockSwitch and Controller
to get clocks from the ClockRegistry. Since the only clock
available from the registry is the default one, this should
have no user-facing changes, and is intended only to update
the relevant codepaths.

Bug: 229771520
Test: Manual and Automated
Change-Id: Ia053aaec6987e00de980388a6c024d8bcf5203a2