timers: remove domain specific code

It is no longer necessary to explicitly set the handle
to inherit the Timeout domain.

PR-URL: https://github.com/nodejs/node/pull/18477
Refs: https://github.com/nodejs/node/pull/16222
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Khaidi Chu <i@2333.moe>
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>

lib/timers.js

@@ -586,7 +586,6 @@ Timeout.prototype.unref = function() {
     this._handle.owner = this;
     this._handle[kOnTimeout] = unrefdHandle;
     this._handle.start(delay);
-    this._handle.domain = this.domain;
     this._handle.unref();
   }
   return this;

test/parallel/test-domain-timers.js

@@ -30,13 +30,19 @@ timeoutd.on('error', common.mustCall(function(e) {
   assert.strictEqual(e.message, 'Timeout UNREFd',
                      'Domain should catch timer error');
   clearTimeout(timeout);
-}));
+}, 2));
 
+let t;
 timeoutd.run(function() {
   setTimeout(function() {
     throw new Error('Timeout UNREFd');
   }, 0).unref();
+
+  t = setTimeout(function() {
+    throw new Error('Timeout UNREFd');
+  }, 0);
 });
+t.unref();
 
 const immediated = domain.create();