Fixing regression in entering PiP over keyguard.

- The call to check the current system state before entering PiP should
  not check the keyguard visibility state when the activity is resumed.
  The caller (enterPictureInPictureMode()) will make that check itself
  and defer until entering PiP until the keyguard is gone.

Bug: 33645392
Test: android.server.cts.KeyguardLockedTests
Test: android.server.cts.ActivityManagerPinnedStackTests
Change-Id: Ib9a5d0f51400b8dd9146e3445c2415e2a458e690