Clean old coexistence get/setApplicationRestrictions.

* The implementation on the else branch is more recent, complete and already in prod.
* Backwards compatibility code is already present in the respective
  enforcement callback.

Test: btest android.devicepolicy.cts.ApplicationRestrictionsTest
Flag: android.app.admin.flags.set_application_restrictions_coexistence
Bug: 369141952
Bug: 336297680
Change-Id: I564856d2372408aef42bc6f702c1d093d2801dd2