lib: remove useless getLibuvNow in internal/timers

PR-URL: https://github.com/nodejs/node/pull/23995


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: Matheus Marchini <mat@mmarchini.me>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Ujjwal Sharma <usharma1998@gmail.com>