Fixes incorrect system app deletion logic

This change corrects a bad boolean check made in a recent refactor that
was causing non-child system packages to be treated as system packages.
It also bypasses the may delete check for replacing system apps as these
are not deleted the same as non-system.

Change-Id: If43a6d019deb0f203a5cfd2c33e02679b05899f3
Fixes: 120213570
Fixes: 120186133
Test: system updates are successful