Fix call stack size exceeded group milestone description autocomplete

What does this MR do?

Remove page-specific init of GLForm that forces autocomplete support functionality.

Explicitly set data-support-autocomplete to false.

Are there points in the code the reviewer needs to double check?

Why was this MR needed?

call stack size exceeded when entering a gfm ref in group milestone description input.

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Review
  • Has been reviewed by UX
  • Has been reviewed by Frontend
  • Has been reviewed by Backend
  • Has been reviewed by Database
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together

What are the relevant issue numbers?

Closes #39020 (closed)