Don't hold AM lock in AMS.getIntentSender

Nothing in the method requires the lock to be held as both the
user controller and pending intent controller have their own locks.
So, safe to remove to avoid deadlock where WM calls into PM which in
turn calls this method.

Change-Id: If91c0fb7477a0b71efce029089e6186b5dac8255
Fixes: 119559831
Test: N/A