Don't hold WM lock while updating OOM adj

Holding the lock can cause quite the performance regression, up
to 9-10ms for app hot launch tests depending on thread
interleaving.

Since the original issue was fixed by
I160f951e103835401ccaaf7c732ba407e011c39b let's try again without
holding the lock since this can be quite a big performance hit.

Test: atest AppTransitionTests
Bug: 123502026
Bug: 124067004
Change-Id: If6bbe35139aeaa3a36d9d1ce5aad2b3503ac95f8
Fixes: 124019557