Revert the process noise co-variance of the bitrate over-use estimator to its value prior to r9545.

R=pbos@webrtc.org
TBR=tommi@webrtc.org
BUG=crbug:508678

Review URL: https://codereview.webrtc.org/1231033002 .

Cr-Commit-Position: refs/heads/master@{#9565}
3 files changed