CategoryTool.getCategoryList dynamically returns categories as member of
themselves, but there were cases (for example after changing id) where
the membership happens to be saved in `categories` attribute and later
caused problems after clones or renames.
To prevent these problems, CategoryTool._setCategoryList detects the
membership to self and does not save it as part of .categories

Remove no longer needed after clone script.

Remove tests which no longer makes sense now that setCategoryList does
not add membership to self.