Remove unused still_running member

Author: nikic

ext/curl/curl_private.h

@@ -116,7 +116,6 @@ typedef struct {
 } php_curlm_handlers;
 
 typedef struct {
-	int         still_running;
 	CURLM      *multi;
 	zend_llist  easyh;
 	php_curlm_handlers handlers;