Remove unnecessary mScreenAcquired

This variable is only used for debugging, and did not have any effect on
behavior. It's also not quite the right information in a multi-display
world.

Factored out of If60218e85292c786b9fa70ecb33ee374d3a385e0. Making this
change simplifies further refactoring in re-landing that CL.

Bug: 255601557
Bug: 256196556
Bug: 241286146
Test: m
Change-Id: I062002245db8fd817e145a3aaf197bb874b00636