openssl: Free modules on cleanup

Curl_ossl_init calls OPENSSL_load_builtin_modules() but
Curl_ossl_cleanup doesn't make a call to free these modules.

Bug: https://github.com/bagder/curl/issues/526

lib/vtls/openssl.c

@@ -746,6 +746,9 @@ void Curl_ossl_cleanup(void)
 #else
   ERR_remove_state(0);
 #endif
+
+  /* Free all memory allocated by all configuration modules */
+  CONF_modules_free();
 }
 
 /*