Removes Sherlock-related configs and docs

What does this Merge Request do and why?

We removed Sherlock entirely, more in the issue: gitlab#349293 (closed) Now, let's remove GDK-related configs & docs.

⚠ depends on gitlab!77345 (merged)

Merge Request checklist

• This change is backward compatible. If not, please include steps to communicate to our users.
• [-] Tests added for new functionality. If not, please raise Issue to follow-up.
• Documentation added/updated, if needed.
• [-] gdk doctor test added, if needed.
• [-] Add the ~highlight label if this MR should be included in the CHANGELOG.md.