Fix missing ASL after reboot

Only clear the appMetadataFilePath in commitPackageSettings if the
lastUpdateTime has changed. Previously we only checked that the old
package setting was null which was not reliable because in many cases
the old package setting is set to be the existing package setting.

Bug: 354882606
Test: Manually add a entry in preinstalled-packages--asl-files.xml for a
system app
Test: adb shell setprop persist.pm.mock-upgrade true && adb reboot
Test: check that the ASL for the system app persists after reboots
Flag: EXEMPT bugfix

Change-Id: Ibbf1be2e3e160eb143393d3eb7bf5fac0e4229a5