bugfix: removed Project.nested_fields

When nested_fields is set on the Model.Meta it overrides the default behaviour of fetching these from Project.nested.fields()

the output from shell is as follows:

>>> Project.nested.fields()
['customerInvoices', 'members', 'communities', 'freelancerInvoices']

customer I believe is correctly excluded because it's a ForeignKey rather than a toMany relationship