Revert "Only show dialog if top app is killed"

This reverts commit 90024ace.

Commens in ag/3029299 for more details.
After this is reverted, ag/2891284 will need to be reverted (for oc-mr1-dev),
and ag/2961224 for master).

Reason for revert: No mechanism to check if an app is killed because of low memory killer

Change-Id: I4aeef4f3008280a34f0b898ed7a2da37be006a84
Bug:65488249