Switch to using AudioEncoderIlbc instead of ACMILBC

This change switches from the old codec wrapper ACMILBC to the new
AudioEncoderIlbc wrapped in an ACMGenericCodecWrapper.

BUG=4228
COAUTHOR=kwiberg@webrtc.org
R=tina.legrand@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/40699004

git-svn-id: http://webrtc.googlecode.com/svn/trunk/webrtc@8314 4adac7df-926f-26a2-2b94-8c16560cd09d