Don't call the Package Manager when holding the settings lock

The package manager sometimes has to call into the settings provider with
its own lock held in the course of processing queries, so it's vitally
important not to call into it with the settings provider's internal lock
already held.

In this case, the SSAID lazy-generation path was fetching the signatures
of the calling package from inside the settings lock.  Now it doesn't.

Bug 36863412
Test: manual

Change-Id: Ic9d53397b5bddb883c5d73aff253ca280a5e93c0