Move BWE period calculation from ProbingIntervalEstimator to AimdRateControl.

Remove the ProbingIntervalEstimator and MockAimdRateControl.

BUG=webrtc:7441

Review-Url: https://codereview.webrtc.org/2789233005
Cr-Original-Commit-Position: refs/heads/master@{#17769}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 6737045af14f3df3537be4c9400936c226601119
12 files changed