Remove remnant of MS SGC second ClientHello.

This code was dead as ssl3_get_client_certificate no longer allows a
ClientHello; the hash would be reset, but then the handshake would fail anyway.

Change-Id: Ib98e6a319c048c263d7ee3a27832ea57bdd0e2ad
Reviewed-on: https://boringssl-review.googlesource.com/2120
Reviewed-by: Adam Langley <agl@google.com>