Revert "Migrate InputMethodService to use OnBackInvokedDispatcher"

This reverts commit 38be9e32f161828b3a8d3f4e0046af3213350622.

Reason for revert: Caused b/229642813 and b/229355440

Bug:229642813
Bug:229636388

Change-Id: I65e4f66ec2156d4e0812753d71ac82afd965fe3b
3 files changed