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>