Revert "[ActivityManager] Avoid keeping restarting home when only home activity exists."

This reverts commit 4ff51c19cc2e37c980ab5bbfcccec083e35a2d82.

Change-Id: I50f05e538c87a01efee09d73c4d5d48ab9b51262
Merge "Revert "[ActivityManager] Avoid keeping restarting home when only home activity exists."" into kitkat3