Useless configure checks for RAND_OpenSSL (HAVE_RAND_OPENSSL)

Hi all,

We have been using RAND_OpenSSL(), a function new as of OpenSSL 1.1.0
in pgcrypto until fe0a0b5 which has removed the last traces of the
function in the tree.  We still have a configure check for it and the
related compilation flag in pg_config.h.in, and both are now useless.

Any objections to the cleanup done in the attached patch?

Thanks,
--
Michael