Remove the soon-to-be-removed Authentiq page from nav
Removes https://docs.gitlab.com/ee/administration/auth/authentiq.html from the left nav. Per Remove omniauth-authentiq gem (gitlab!110259 - merged) the company behind this auth method has gone out of business, so the auth method is already gone. We're truncating the page per https://docs.gitlab.com/ee/development/documentation/versions.html#remove-a-page and we might as well get it out of the left nav, too.
Awareness to @jglassman1 as the TW for ~"group::authentication and authorization", and @ifarkas + @dstull because they're involved with the page-removal MR.
Related to Deprecate / remove omniauth-authentiq gem (gitlab#389452 - closed)