Separate the wow_item field declaration from the wow_item module itself.

Separate the wow_item field declaration from the wow_item module itself, this will removes the bug that prevent to uninstall the wow_item module. Due to a bug in D7 (#1284332: Module cannot be disabled because Drupal claim "Field type(s) in use") if you install the wow_item module, you will not be able to uninstall it.
A field is used to handle serveral locales for the item entity, and the module declaring the field use it in the same time. This will be fixed in a future patch and already fixed in D8 (#943772: field_delete_field() and others fail for inactive fields).