No more flush for view tree events.

Background: after API B, there is a dedicated flush event after the traversal. No need to flush the view tree events anymore.

This can help to reduce the binder transactions of `IContentCaptureDirectManager#sendEvents`.

Also cleaned up the launched flag `flush_after_each_frame`.

Bug: 433614684
Flag: android.view.contentcapture.flags.reduce_binder_transaction_enabled
Test: atest FrameworksCoreTests:android.view.contentcapture.MainContentCaptureSessionTest

Change-Id: I11f5ee4c54b8c96399a0355f0e0f8f354adcebca