Header height padding added to layout-page on terms page

from: !129574 (comment 1519279668)

An extra 48px of padding-top is added to the terms page .layout-page from --header-height.

--header-height is set to 0px based on show_super_sidebar? condition in application.html.haml https://gitlab.com/gitlab-org/gitlab/-/blob/16d3f70efb8f371fe49a87213e48d160bfe30ae7/app/views/layouts/application.html.haml#L15-20

In the terms page the old header didn't appear to render, so extra padding-top is not required.

Suggest to refactor how/where --header-height value is set/reset to be more robust for conditional height being added. Note: there are many uses of $header-height (which is set to 48px but default in var(--header-height, 48px)) in other calculations/styles so any foundational changes of this value will need to be validated.

To view terms page:

1. Login as an admin (root user in GDK).
2. Navigate to /admin/application_settings/general
3. In the Terms of Service and Privacy Policy panel:
   1. Check the All users must accept the Terms of Service and Privacy Policy to access GitLab checkbox
   2. Enter some text in the text area
   3. Save the form
4. Navigate to /admin/users and choose a user.
5. Click Impersonate in the upper right corner.