Remove remnants of old OCSP stapling API.

Probably we'll want some simpler server-side API later. But, as things
stand, all consumers of these functions are #ifdef'd out and have to be
because the requisite OCSP_RESPONSE types are gone.

Change-Id: Ic82b2ab3feca14c56656da3ceb3651819e3eb377
Reviewed-on: https://boringssl-review.googlesource.com/4551
Reviewed-by: Adam Langley <agl@google.com>