Fix a no-op uninstall being treated as a failure

Treat a stageUninstall() doing nothing as a success, not a
failure. This prevents the system retrying the uninstall
later.

Modified several tests accordingly and added new
ones to catch similar cases.

Test: Manual testing, adb dumpsys timezone
Test: PTS: run pts -m PtsTimeZoneTestCases
Test: CTS: run cts -m CtsLibcoreTestCases -t com.android.timezone.distro.installer.TimeZoneDistroInstallerTest
Bug: 65657176
Merged-in: I00b0cae4e2473a2b55480f0274af493bbc4f3ca8
Change-Id: I00b0cae4e2473a2b55480f0274af493bbc4f3ca8
(cherry picked from commit 5a9e9b9e)