multi: don't expire timeouts at disonnect or done

The functions Curl_disconnect() and Curl_done() are both used within the
scope of a single request so they cannot be allowed to use
Curl_expire(... 0) to kill all timeouts as there are some timeouts that
are set before a request that are supposed to remain until the request
is done.

The timeouts are now instead cleared at curl_easy_cleanup() and when the
multi state machine changes a handle to the complete state.

lib/multi.c

@@ -1594,6 +1594,8 @@ static CURLMcode multi_runsingle(struct Curl_multi *multi,
       /* Important: reset the conn pointer so that we don't point to memory
          that could be freed anytime */
       easy->easy_conn = NULL;
+
+      Curl_expire(data, 0); /* stop all timers */
       break;
 
     case CURLM_STATE_MSGSENT: