Remove unmigratable old nav specific specs

What does this MR do and why?

This removes unmigratable old top-nav specs:

1. top_nav_responsive_spec.rb tests the special responsive behaviour which we do not have any longer
2. top_nav_spec.rb tests a "Invite members" link from the "Create new" menu. We haven't ported this behaviour yet.
3. top_nav_tooltip_spec.rb tests some tooltip behaviour and is quarantined completely

Screenshots or screen recordings

No user-visible changes

How to set up and validate locally

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