Enable AudioProcessing48kHzSupport by default

Because of the Finch experiment, this will not affect Chrome's behaviour at all.
The SNRs in AudioProcessingTest.Formats were only increased to the next multiple of 5.

BUG=webrtc:3146
R=andrew@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/43359004

Cr-Commit-Position: refs/heads/master@{#9263}
4 files changed