Modify conditions for preventing updated system apps from being downgraded

Add two conditions prior to deciding whether a specific user can
downgrade system apps by deletePackageX.

1.uninstalledPs must be a updated system app.
2.deleteFlags does not contains PackageManager.DELETE_SYSTEM_APP,
since flag PackageManager.DELETE_SYSTEM_APP will just mark the app
as uninstalled for the specific user instead of uninstalling the
update and rolling back to the older system version.

Bug: 236578018
Test: atest DeletePackageHelperTest
Change-Id: I55a3d322e84aaaced69bd5edeaf90e82ac9a0dd3