Remove double-posting in DisplayImeController

Now that the PerDisplay methods already run on the mMainExecutor,
we no longer need to post to that executor from PerDisplay's methods.

Fixes: 175954493
Test: atest DisplayImeController
Change-Id: Ib528b899b7f47f5c4afe3e31925bfb8d8abb8aef
2 files changed