Move duplicateLookup() method back to filehash service

@SpaceGoat1701 how about if we move it back to the main FileHash class for backwards-compatibility reasons, rather than creating a new standalone service?

I had thought there might have been other reasons for removing the functionality from the main FileHash class. But if not, or if those reasons don't supersede backwards-compatibility in your eyes, then I certainly have no problem with moving the functionality back to the main FileHash service.

The method simply moved from one class to the other for consolidation purposes, but it seems useful to leave it in the main class both for backwards compatibility and to make clear that it can be used as an "API" method.

Automatically closed - issue fixed for 2 weeks with no activity.