http: convert utcDate to use setTimeout

A sort-of follow-up to https://github.com/nodejs/node/pull/17704, this
removes the last internal use of enroll().

PR-URL: https://github.com/nodejs/node/pull/17800


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Evan Lucas <evanlucas@me.com>
Reviewed-By: Minwoo Jung <minwoo@nodesource.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>