Move signal locking Keystore

Move the call to have Keystore lock its internals from
UserController to LockSettingsService. Functionally doesn't change
anything, but as LockSettingsService is already responsible for
signaling to unlock Keystore, it makes sense to keep said communication
centralized in the the LockSettingsService system service.

Bug: b/389069078
Flag: com.android.server.flags.keystore_in_memory_cleanup
Test: atest UserControllerTest w/setprop fw.stop_bg_users_on_switch -1
Test: atest StorageManagerServiceTest
Change-Id: I1469a4d2d61528236190ee9dd74aa69d1e37c481