Add a flag to virtual display to indicates that content on this

display need to be destroyed once the display is removed.
Then apply this flag to VR virtual display.

Change-Id: Icb5aa1280b6ebac5941afda1cc1b94b258ce44f4
Bug: 67420451
Test: Manually. "adb shell am stack list" does not show contents
from virtual display anymore after it's released.