Always install APEX packages

* APEX packages should always be installed and need no
explicit allowlist.

* Don't report errors when APEX is not on allowlist.

Bug: 225756739
Fix: 225756739
Test: atest AndroidCarApiTest
      adb shell cmd user report-system-user-package-whitelist-problems \
      --critical-only --mode 1
      check no errors are reported
Change-Id: Ibfc3c7f4ddb67882005b10af676949b79f034be8