When audio_processing_fuzzer runs with 'DCHECK_ALWAYS_ON', it crashes when both AEC and AECM is enabled at the same time. This change detects that case and fixes https://clusterfuzz.com/v2/testcase-detail/6389429496446976. It also removes an unnecessary safeguard that didn't allow fuzzing with 8kHz input signals. Bug: chromium:776358 Change-Id: I33c18a2a235e50ae410f7be24637872823e432eb Reviewed-on: https://webrtc-review.googlesource.com/15320 Reviewed-by: Patrik Höglund <phoglund@webrtc.org> Commit-Queue: Alex Loiko <aleloi@webrtc.org> Cr-Commit-Position: refs/heads/master@{#20428}