Revert 5228 "Use the RTT from RtcpRttStats class if provided whe..."

> Use the RTT from RtcpRttStats class if provided when sending/receiving NACK.
> 
> R=holmer@google.com
> 
> Review URL: https://webrtc-codereview.appspot.com/5049004

TBR=asapersson@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/5799004

git-svn-id: http://webrtc.googlecode.com/svn/trunk/webrtc@5285 4adac7df-926f-26a2-2b94-8c16560cd09d
3 files changed