Undeprecate OPENSSL_VERSION_NUMBER and OpenSSL_version_num()

Undeprecate OPENSSL_VERSION_NUMBER and OpenSSL_version_num()

This macro and function were deprecated in the documentation but not in
the source.

Following an OTC vote the deprecation has been removed from the
documentation.

See https://github.com/openssl/technical-policies/issues/26

Fixes #17517

Reviewed-by: Tim Hudson <tjh@openssl.org>
Reviewed-by: Paul Dale <pauli@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/17750)

(cherry picked from commit 42659159f4d4a8c16a0e9b089d40a5831b60cbb6)