Remove unused asdf diagnostics

What does this merge request do and why?

• Remove unused asdf-related diagnostics

Closes: #2944 (closed)

How to set up and validate locally

• Ensure gdk doctor still runs successfully

Merge request checklist

• This MR references an issue describing the change.
• This change is backward compatible. If not, please include steps to communicate to our users.
• Tests added for new functionality. If not, please raise an issue to follow-up.
• Documentation added/updated, if needed.
• Announcement added, if change is notable.
• gdk doctor test added, if needed.