timers: simplify clearTimeout & clearInterval

Remove unnecessary condition from timeout & interval clearing.

PR-URL: #18579
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>

lib/timers.js

@@ -465,8 +465,8 @@ function rearm(timer, start = TimerWrap.now()) {
 
 
 const clearTimeout = exports.clearTimeout = function(timer) {
-  if (timer && (timer[kOnTimeout] || timer._onTimeout)) {
-    timer[kOnTimeout] = timer._onTimeout = null;
+  if (timer && timer._onTimeout) {
+    timer._onTimeout = null;
     if (timer instanceof Timeout) {
       timer.close(); // for after === 0
     } else {