TMMBN was capped by configured max bitrate for no apparent reason. Removing this to not require payload-type reconfiguration on new video-codec settings. Actual removal of payload-type reconfiguration will happen in a pending CL. BUG=webrtc:5494 R=stefan@webrtc.org Review URL: https://codereview.webrtc.org/1702043002 . Cr-Commit-Position: refs/heads/master@{#11639}