Remove CountDownLatch from AssistReceiver.

We track whether inline request is needed with a separate boolean. This
also resolve the bug where the CountDownLatch was accounting for both
inline and regular request, and errors when due to async on multiple
requests, receives multiple regular request instead.

Bug: 162357598
Fixes: 159417365
Test: atest CtsAutoFillServiceTestCases
Change-Id: I56e11163d9163f73f807f6adf06d93bf26617173