doc: remove confusing reference in governance doc

At the CTC meeting today, Sakthipriyan noted that there was a link to
the CTC consensus material from the pull request consensus material. The
link was confusing because the CTC consensus material is
meeting-specific, which does not apply to pull requests. I have removed
that link and replaced it with a text explanation.

PR-URL: https://github.com/nodejs/node/pull/9073


Reviewed-By: Myles Borins <myles.borins@gmail.com>
Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: James M Snell <jasnell@gmail.com>