doc: remove GA tracking

The Google Analytics tracking wasn't wholly uncontroversial and hasn't
been used in practice. Remove it.

PR-URL: https://github.com/nodejs/node/pull/23083
Fixes: https://github.com/nodejs/node/issues/22652
Refs: https://github.com/nodejs/node/pull/6601


Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Roman Reiss <me@silverwind.io>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Refael Ackermann <refack@gmail.com>
Reviewed-By: Сковорода Никита Андреевич <chalkerx@gmail.com>
Reviewed-By: Anna Henningsen <anna@addaleax.net>