The method is no longer used, since the jitter buffer delay is
obtained directly from AudioCodingModule instead of being calculated
and smoothed in VoiceEngine. Deleting a few obsolete member variables
as well.
BUG=webrtc:6237
Review-Url: https://codereview.webrtc.org/2290253002
Cr-Commit-Position: refs/heads/master@{#14007}