[Meta Workflow] Finish the WorkflowMetaTypeVersion refactor cleanup

[JoaoRoxoNeves]

The WorkflowMetaTypeVersion refactor was abandoned half-way through.

Before any further developments on the meta-workflow, it is important to finish this refactor and perform a major cleanup on the code.

• Remove old comments of code or domain from before the refactor.
• Remove unused domain slots and relations from before the refactor AFTER MAKING SURE THE DATA WAS CORRECTLY MIGRATED
• Refactor and simplify the remaining code for clarity.