Experiment Cleanup: Remove the `pql_three_cta_test`

Summary

• Experiment key / feature flag name: pql_three_cta_test
• Experiment results: Full results can be found here but TLDR:
  • Due to changes to the navigation in the past year and plans to introduce the super sidebar, we should clean up this experiment and remove all code related. The following high level analysis can be used for future projects if appropriate.
• Epic or issue link: #337551 (closed)

Changes to implement as part of the roll out to becoming an official part of the product:

We want to remove this experiment completely.

Steps

• Determine whether the feature should apply to SaaS and/or self-managed
  • n/a as we are removing
• Determine whether the feature should apply to EE - and which tiers - and/or Core
  • n/a as we are removing
• Determine if tracking should be kept as is, removed, or modified.
  • Removed
• Ensure any relevant documentation has been updated.
  • No documentation updates needed
• Consider changes to any feature_category: introduced by the experiment if ownership is changing (PM for Growth and PM for the new category as DRIs)
  • n/a as we are removing
• Check to see if the experiment introduced new design assets. Add them to the appropriate repos and document them if needed.
  • n/a as we are removing
• Optional: Migrate experiment to a default enabled feature flag for one milestone and add a changelog. Converting to a feature flag can be skipped at the ICs discretion if risk is deemed low with consideration to both SaaS and (if applicable) self managed
  • n/a as we are removing
• In the next milestone, remove the feature flag if applicable
• After the flag removal is deployed, clean up the feature/experiment feature flags by running chatops command in #production channel
• Ensure the corresponding Experiment Rollout issue is updated
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