Ensure SafetySourceReceiver only runs for system user

This prevents a new phone process from being launched for every user (including guests)

Bug: 330095930
Test: manually: build, switch to guest user, assert no new phone process
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:48b381197558414b13efc74cee82747c7fe1369d)
Merged-In: If49ebd97dff1844d0918587fa513473de296d23a
Change-Id: If49ebd97dff1844d0918587fa513473de296d23a
1 file changed