Revert "Add project_runners_vue_ui feature flag"

What does this MR do and why?

Revert "Add project_runners_vue_ui feature flag"

This feature is not prioritized and there are no plans to expand on the project runners currently. Removing this feature from the codebase.

This reverts commit a45145e7.

Changelog: other

Screenshots or screen recordings

NA

How to set up and validate locally

No steps required, the feature flag is removed and it was not in use.

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 #33803