Retire the dalvik.vm.useartservice system property.

Using the legacy dexopt implementation in PackageManager is no longer
an option in VIC. This removes most of the legacy code, with these
exceptions:

- OtaDexoptService is still in use, so keep the code it uses in
  PackageDexOptimizer.

- LegacyDexoptDisabledException is kept for the code paths above. All
  other uses of it are removed.

- DexOptHelper.performDexOptMode is used from vendor code, so keep it
  for now. Also keep the code to convert legacy flags to ART Service
  flags - this will be addressed in a later CL.

- DexManager and PackageDexUsage will be addressed in a later CL.

- More cleanups of unused code in Installer, DexOptHelper,
  DexoptOptions, and various other places will be addressed in later
  CLs.

Test: atest FrameworksServicesTests FrameworksMockingServicesTests
Test: m dist
      system/update_engine/scripts/update_device.py \
        out/dist/cf_x86_64_phone-ota-mast.zip
      adb shell setprop persist.pm.mock-upgrade true
      adb reboot
Bug: 258223472
Change-Id: I84b59331dcd1eee6ed2f61f734a6a635d2acdeb1