These are completely unused, but for BIO_set_write_buffer_size which is
in some (unreachable) nginx codepath. Keep that around so nginx
continues to build, but otherwise delete it.

Change-Id: I1a50a4f7b23e5fdbc7f132900ecacd74e8775a7f
Reviewed-on: https://boringssl-review.googlesource.com/13362
Reviewed-by: David Benjamin <davidben@google.com>
Commit-Queue: David Benjamin <davidben@google.com>
CQ-Verified: CQ bot account: commit-bot@chromium.org <commit-bot@chromium.org>