Rename the adapt audio bitrate experiment.
Rename the adapt audio bitrate experiment.

BUG=webrtc:5079

Review-Url: https://codereview.webrtc.org/2498233003
Cr-Original-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#15080}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: b2b61b359c804f5dc237b387e40fc709798ce5dc

Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk