Merge r1781187, r1781190, r1781312 from trunk:

mod_ssl: work around leaks on (graceful) restart.

Tested with valgrind and --with-ssl shared/static.


mod_ssl: follow up to r1781187.
The ssl_util_thread_*() functions are not necessary with openssl-1.1+


mod_ssl: follow up to r1781187.
Address SSL_CTX leak in (merged) proxy_ctx.


Reviewed by: ylavic, jim, wrowe


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1788442 13f79535-47bb-0310-9956-ffa450edef68