Remove AgcManager.

It was not used anywhere.

R=andrew@webrtc.org

Review URL: https://codereview.webrtc.org/1299143003 .

Cr-Original-Commit-Position: refs/heads/master@{#10113}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: d094c04baffabfa914682050615b97faea939bd1
14 files changed