Clean the former submodules after fetch.

This is a general Merge Request template. Consider to choose a template from the list above if it will match your case more.

What does this MR do?

It removes the former submodules that were in the revision before fetching and had deleted in the revision after fetcing.

Why was this MR needed?

Because we have garbage in the working directory when use the fetch-strategy

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

Does this MR meet the acceptance criteria?

• Documentation created/updated
• Tests
  • Added for this feature/bug
  • All builds are passing
• Branch has no merge conflicts with master (if you do - rebase it please)

What are the relevant issue numbers?