Revert a couple of badly-behaving ActivityManager patches.

 * These patches together are causing a bit of havoc. Killing processes
   on the background thread often means the death takes longer,
   increasing the likelyhood of the kernel obliterating it on it's own.
   Instead of the nice happy shutdown by AM, the kernel ends up
   following up the slaughter with direct reclaim, wrecking system
   performance. This is even more apparent on low-ram systems.

 * Additionally, don't encourage services to spuriously restart as the
   second patch is doing. This compounds the problem from the first
   patch.

Revert "KillProcessGroup on background thread"

This reverts commit 5d1a70a4.

Revert "[ActivityManager] Bring up Service if not schedule to restart"

This reverts commit 4fd268b8.

Change-Id: I53ca87009d066c87bf50bde25558431f6bf74bca