Update references to RFCs.

Some code predated the RFCs themselves, but the RFCs now exist. Also remove
now obsolete comments and some unused #defines.

See upstream's cffeacd91e70712c99c431bf32a655fa1b561482. (Though this predates
it; I just remembered I never uploaded it.)

Change-Id: I5e56f0ab6b7f558820f72e84dfdbc71a8c23cb91
Reviewed-on: https://boringssl-review.googlesource.com/2475
Reviewed-by: Adam Langley <agl@google.com>
4 files changed