Fake ae precapture cancellation when requested

Limited devices are expected to have precapture ae enabled and
respond to cancellation request. Since we don't actuall support
AE at all, let's just respect the cancellation expecation in
case it's requested

Fixes: 333865684
Test: StillCaptureTest#testAePrecaptureTriggerCancelJpegCapture
Change-Id: I863219bc8740307ebf93d43c9b2f9b71eb683c9a