Revert "use event_free() wrapper; fix bug 4582"

This reverts commit 9a88c0cd.

src/common/compat_libevent.c

@@ -573,7 +573,7 @@ run_runnable_cb(evutil_socket_t s, short what, void *arg)
   void *cb_arg = r->arg;
   (void)what;
   (void)s;
-  tor_event_free(r->ev);
+  event_free(r->ev);
   tor_free(r);
 
   cb(cb_arg);