Remove non-functional asynchronous resampling mode.

A few other cleanups, most notably using a sane parameter to specify the
number of channels.

BUG=chromium:469814
R=tina.legrand@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/46729004

Cr-Original-Commit-Position: refs/heads/master@{#8894}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 2c9c83d7ecd7251362d438abc70c9f50b208f316
8 files changed