Remove redundant code block

This block never fires as it appears to be missing an each.
The first line of the block would raise a method_missing exception if it did execute.
related_request.asset = target_asset in all cases, so the block is completely redundant anyway

I can only assume it was supposed to walk down the request graph, but even then what I can only suppose was intended to be a recursive remove_unused_assets call would cover everything.

But the block has been entirely non-functional for three years, and redundant since the move to git. So I'm nuking it, as restoring the intended behaviour based on guesswork is just going to cause trouble; leaving the code here is just going to cause headaches.