Revert "Fix: avoid assignment discards 'const' qualifier warning"

This reverts commit 0dbabcc4.
Breaks other OpenSSL versions.

src/connection.c

@@ -188,7 +188,7 @@ static unsigned long _next_connection_id(void)
 #ifdef HAVE_OPENSSL
 static void get_ssl_certificate (ice_config_t *config)
 {
-    const SSL_METHOD *method;
+    SSL_METHOD *method;
     long ssl_opts;
     ssl_ok = 0;