Since PHP 7.4, the PHP_SETUP_OPENSSL autoconf macro completely relies on pkg-config and no longer utilizes $PHP_OPENSSL_DIR to search for OpenSSL headers. This change was implemented in php/php-src@fe8fdfa.

Prior to PHPC-888, which introduced support for alternative TLS libraries, we utilized the PHP_SETUP_OPENSSL macro directly. In mongodb/mongo-php-driver@d679bfe, we removed that macro but ported the directory search logic to CheckSSL.m4.

This should be removed so that we can depend on pkg-config as is done in PHP 7.4+.

We might still want to leave the PHP_CHECK_LIBRARY code in place (else condition of PKG_CHECK_MODULES) if that is ultimately necessary for FreeBSD compatibility.