Remove Windows XP SHA-256 and ECDSA logic.

We can assume the system verifier handles both SHA-256 and ECDSA now.
No need to inject SHA-256 support or disable ECDSA ciphers.

BUG=554410

Review URL: https://codereview.chromium.org/1610833004

Cr-Commit-Position: refs/heads/master@{#371329}
16 files changed