Remove usages of package-scanning bugfix flags.

This is allowed per official flag cleanup policy for bugfix flags.

- scan_packages_without_lock is already in Nextfood
- deprecate_package_list_observer has been in Trunkfood Full for
  3 months.

Bug: 295969873
Bug: 304561459
Test: AccessibilityManagerServiceTest in presubmit
Change-Id: Ice83118d74932168e861349a8e43d2d121059ed3