Remove code and update Readme to warn about repo move. Refs #14

What does this MR do?

Remove all code and only leave README with note about project move.

Why was this MR needed?

gl-sast repository has been moved to security-products subgroup

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• Tests added for this feature/bug
• Has been reviewed by other person

What are the relevant issue numbers?

#14