Remove explain_vulnerability_tool feature flag

What does this MR do and why?

WIP: Remove explain_vulnerability_tool feature flag

Changelog: changed EE: true

MR acceptance checklist

⚠ Required Manual Check from a member of the TI team @alexbuijs @darbyfrey @dpisek @sming-gitlab ⚠

• Copy the checklist from this issue: FF Cleanup Manual Test Checklist (#478761 - closed)
• Paste the items as a comment in this MR
• Complete all the manual checks

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

Before	After

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

Related to #471732 (closed)