Move mock_nonlinear_beamformer to only be a header

webrtc/modules/audio_processing/beamformer/mock_nonlinear_beamformer.cc

-/*
- *  Copyright (c) 2015 The WebRTC project authors. All Rights Reserved.
- *
- *  Use of this source code is governed by a BSD-style license
- *  that can be found in the LICENSE file in the root of the source
- *  tree. An additional intellectual property rights grant can be found
- *  in the file PATENTS.  All contributing project authors may
- *  be found in the AUTHORS file in the root of the source tree.
- */
-
-#include "webrtc/modules/audio_processing/beamformer/mock_nonlinear_beamformer.h"
-
-#include <vector>
-
-namespace webrtc {
-
-MockNonlinearBeamformer::MockNonlinearBeamformer(
-    const std::vector<Point>& array_geometry)
-    : NonlinearBeamformer(array_geometry) {
-}
-
-}  // namespace webrtc