Cleanup after moving test/fake_audio_device to
modules/audio_device/include/test_audio_device.
Hide implementation of test audio device module in the anonymous namespace.
Bug: webrtc:8946
Change-Id: I2d49c3ec5d43eeb5f155d38de95f69ed3c537805
Reviewed-on: https://webrtc-review.googlesource.com/61426
Commit-Queue: Artem Titov <titovartem@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#22401}