Delete unused file mock_audio_vector.h.

BUG=webrtc:6424

Review-Url: https://codereview.webrtc.org/2367323002
Cr-Original-Commit-Position: refs/heads/master@{#14388}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: c637389949a81f6a91557d78576c3ef95219c26c
2 files changed