mod_ssl: Switch to using OpenSSL's automatic internal DH parameter

mod_ssl: Switch to using OpenSSL's automatic internal DH parameter
generation from OpenSSL 1.1.0 and later.  The
SSL_set_tmp_dh_callback() API is deprecated from OpenSSL 3.0 onwards.
Should not be a user-visible change (except mod_ssl gets smaller).

* modules/ssl/ssl_private.h,
  modules/ssl/ssl_engine_kernel.c,
  modules/ssl/ssl_engine_init.c (ssl_init_ctx_callbacks):
  Drop internal DH parameter generation and callback for OpenSSL 1.1+,
  use SSL_CTX_set_dh_auto(, 1) instead.

Github: closes #188
Reviewed by: rpluem

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1890067 13f79535-47bb-0310-9956-ffa450edef68