Temporaly ignoring UID check when caller is a system app.

The Settings app runs some of its activities in another process, which would
crash it in some cases due to a recent security fix on Autofill.

This CL temporarily fixes the problem by skipping the security check when the
caller is a system app.

Test: manual verification using System.out statements, as it cannot be
      reproduced by CTS because the CTS app is an user app.
Bug: 70506888

Change-Id: I08e8a370d93d3473ec5e025afaf3bc6f456e0ab9