Remove DISPATCH_BACK_INVOCATION_AHEAD_OF_TIME.

We are not gating the new back dispatch by targetSdkVersion in T. The new dispatch is controlled by the enableOnBackInvokedCallback app
manifest flag (which defaults to false).

Test: m -j update-api
Bug: 195946584
Change-Id: Iab59051ec5b6336ca4d42cc47015fe86a3f37942
3 files changed