Suppressing warnings in GetRTT() in VoE.

GetRTT() was separated from GetRTPStatistics() but the warnings were not updated.

Now GetRTT() is only only used by GetRTPStatistics() and the warning pops up pointlessly and too often.

This CL is to suppress these warnings and maintain a proper warning for GetRTPStatistics().

BUG=
R=henrika@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/36469004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@7899 4adac7df-926f-26a2-2b94-8c16560cd09d