Remove nonfunctional jtr_unshadow

The Credential changes made JtR both deprecated and non-functional. It used to be useful because linux hashdump functions dumped hashes into loot instead of saving them as creds. Now, when a user does a hashdump on linux, it already unshadows, saves those items as credential objects.

This means that jtr_unshadow has been pretty much vestigal. It should have used the Deprecated mixin and pointed to a module that ended up doing the same thing, but that's neither here nor there.

No verification steps are needed, as this is simply removing a module that has been doing nothing for months anyway.