Global Search New Navigation - part 3

What does this MR do and why?

This MR tweaks the last small-ish visual issues to implement this according to designs. It removes the scope nav and filters horizontal dividers and the size of the header font. This is conditional on whether the new left navigation is enabled.

MR sequence	status
1. Global Search New Navigation - fundation	in review
2. Global Search New Navigation - part 1	in review
3. Global Search New Navigation - state	in review
3. Global Search New Navigation - part 2	in review
4. Global Search New Navigation - part 3	in review 👈 this

Screenshots or screen recordings

before	after

How to set up and validate locally

1. Setup the Advanced Search https://gitlab.com/gitlab-org/gitlab-development-kit/blob/main/doc/howto/elasticsearch.md
2. Enable the Advanced Search http://gdk:3000/admin/application_settings/advanced_search
3. Enable and turn on the new left sidebar
4. Visit the search page: http://gdk:3000/search

Validation:

1. Visit the search page: http://gdk:3000/search with Advanced Search enabled
2. Visit the search page with Advanced Search disabled
3. Test the code search for filters
4. Test the issues search for filters

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #382328 (closed)