Get version-related functions from crypto.h rather than ssl.h.

(This makes it possible to include opensslv.h when not linking SSL.)

Change-Id: Id88c5ff44a7099d33d8d4672f7ba88986ffd1526
Reviewed-on: https://boringssl-review.googlesource.com/4831
Reviewed-by: Adam Langley <agl@google.com>