Hi,

I think you cannot delete the models from the User interface ,

see the unlink function that raises the the above warning.

@api.multi
def unlink(self):
    # Prevent manual deletion of module tables
    if not self._context.get(MODULE_UNINSTALL_FLAG):
        for model in self:
            if model.state != 'manual':
                raise UserError(_("Model '%s' contains module data and cannot be removed!") % model.name)

    self._drop_table()

Thanks