Fix widget manager / alarm manager deadlock

Don't hold locks while manipulating alarms within the app widget
server, because the joint dependencies on activity manager locking
cause problems.

Change-Id: Ic7a09e6938277df7201be515f9785f326552f166
Bug: 115894687
Test: manual (repeated rebooting including with alarms forced)
(cherry picked from commit fb2f70a6)