capture_mode: Remove wrong DCHECK

It was added by mistake by me. It is possible to get
audio frames after we delete the capturer, since
they're sent asynchronously from a different thread.

BUG=1154087
TEST=None

Change-Id: I297cbb7a2373e716dd5a46e7eb9f406914e059ad
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2566717
Auto-Submit: Ahmed Fakhry <afakhry@chromium.org>
Reviewed-by: Sammie Quon <sammiequon@chromium.org>
Commit-Queue: Ahmed Fakhry <afakhry@chromium.org>
Cr-Commit-Position: refs/heads/master@{#832420}

ash/services/recording/recording_service.cc

@@ -332,7 +332,6 @@ void RecordingService::OnAudioCaptured(
     base::TimeTicks audio_capture_time) {
   DCHECK_CALLED_ON_VALID_THREAD(main_thread_checker_);
   DCHECK(encoder_muxer_);
-  DCHECK(audio_capturer_);
 
   // We ignore any subsequent frames after a failure.
   if (did_failure_occur_)