Merge branch 'leipert-remove-top-nav-haml-code' into 'master'

Remove old marketing header and top nav code

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/138341



Merged-by: Douglas Barbosa Alexandre <dbalexandre@gmail.com>
Approved-by: Andrew Fontaine <afontaine@gitlab.com>
Approved-by: Andrei Zubov <azubov@gitlab.com>
Approved-by: Max Orefice <morefice@gitlab.com>
Approved-by: Douglas Barbosa Alexandre <dbalexandre@gmail.com>
Reviewed-by: Max Orefice <morefice@gitlab.com>
Co-authored-by: Lukas Eipert <leipert@gitlab.com>