Print correct version code when skipping outdated system packages

When a newer version of a package exists on /data, the package manager
will skip scanning the outdated version on /system. As part of this the
following is printed to logcat:

    Package <name> at <path> ignored: updated version <new-version>
    better than this <old-version>

Teach the package manager to read <new-version> from the correct
variable (it used to be identical to <old-version>).

Bug: 78871949
Test: manual (upgrade a pre-installed app, check logcat on reboot)
Change-Id: Iaa4e43d2f91ca33a0e56e90c233d5d02abed781e