Remove free that could segfault.

cgminer.c

@@ -4285,7 +4285,6 @@ retry_stratum:
 	 * and if so, switch to that in preference to getwork if it works */
 	if (pool->stratum_url && stratum_works(pool)) {
 		applog(LOG_NOTICE, "Switching pool %d %s to %s", pool->pool_no, pool->rpc_url, pool->stratum_url);
-		free(pool->rpc_url);
 		pool->rpc_url = strdup(pool->stratum_url);
 		pool->has_stratum = true;
 		curl_easy_cleanup(curl);