Revert "Distinguish warm/hot launch by whether the activity has attached process"

This reverts commit 20efc15c.

Reason for revert: Droidcop: Potential culprit for Bug b/171719665 - verifying through Forrest before revert submission. This is part of the standard investigation process, and does not mean your CL will be reverted.

Merged-In: I18e2f1a5eaf1e07b96d6135be56f8077d37b7504
Change-Id: I46d622d34a984bf40fe9cbb4a6454e41861d8027