Remove deprecated git clean strategy

What does this MR do?

Removes support for deprecated git clone strategy.

Why was this MR needed?

Please read #4175 (closed) for details

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

Does this MR meet the acceptance criteria?

• Documentation created/updated
• Added tests for this feature/bug
• In case of conflicts with master - branch was rebased

What are the relevant issue numbers?

Closes #4175 (closed)