pm shell command to uninstall system updates

This change introduces a new package manager shell command that
will automatically uninstall any updated system apps, falling back
to the version that is prebaked into the system image.

Change-Id: Ic2952394baadeea6286e0a87343201e564ffdfb9
Fixes: 21088599
Test: manual - run before SUW and after; see updates uninstalled
1 file changed