Disable super_sidebar_nav_enrolled feature flag locally in specs

What does this MR do and why?

We currently disable the super_sidebar_nav_enrolled feature flag globally in specs. Over a few MRs we have introduced a user trait which disables the feature flag on a per-spec basis:

• !130148 (merged)
• !130151 (merged)
• !130301 (merged)
• !130302 (merged)

This commit removes the global feature flag toggle and makes a few remaining specs pass.

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The full plan is to:

1. Introduce a user specific trait and move from a global "old"-nav switch to a per-test switch:
   • Introducing the trait !130148 (merged)
   • At least three more MRs: !130151 (merged), !130301 (merged), !130302 (merged)
   • This MR switching to per-test
2. Remove the global feature flag toggle (MR to be raised)
3. Fix all tests to work with the new nav: #420121 (closed)
4. Remove the trait

Screenshots or screen recordings

N/A

How to set up and validate locally

1. Log-in as a user who doesn't have the new-nav setting enabled explictly. They should see the new navigation.

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.