Remove dream when keyguard going away

The old removal method by doing it in handleRequest won't work as the
shell initiated transition is expected to have everything in WCT ready
before start, and the handleRequest will never be called.

Thus, to properly remove the dream in the same WCT, include it before
start the transition.

Bug: 364930619
Test: Dream is properly removed when the flag is enabled
Flag: com.android.window.flags.ensure_keyguard_does_transition_starting
Change-Id: I7c31dd9a2c83d43a77464c89776b3d8475e243f4