Unwind the fallback admin policy knobs.

Part 1 of removing the TLS version fallback code. Later commits will unwind
other pieces.

The admin policy has expired, so there is no need to keep the code around.

BUG=621780

Review-Url: https://codereview.chromium.org/2098723002
Cr-Commit-Position: refs/heads/master@{#402310}
11 files changed