Remove remnants of KRB5 support.

This drops the bits of logic that allowed Certificate messages to be optional
for a KRB5 cipher suite.

Change-Id: I2a71b7c13d7e76f4f5542d4074169f80f3617240
Reviewed-on: https://boringssl-review.googlesource.com/1154
Reviewed-by: Adam Langley <agl@google.com>
7 files changed