Fix a bug in UserSystemPackageInstaller#installWhitelistedSystemPackages

When userWhitelist was not null, it only mutated the packages in
userWhitelist, and other packages left untouched.
The correct behavior is to iterate all packages and install or
uninstall according to userWhitelist.

BYPASS_INCLUSIVE_LANGUAGE_REASON=existing code that cannot be changed

Bug: 234877652

Test: atest UserSystemPackageInstallerTest
Test: Manual test with gcar_emu_x86_64 emulator

Change-Id: I4325565d8acaeffd4aab5a4b6295d325edb738a9