I am using odoo8, and I just created one field for model which is inherited from res.partner in py file. After i upraded the module, the field was generated in model res.partner. This is as expected. 

After a while I found the field which i just created is not needed actually, so I remove the code for the field in py file, and restarted server/upgraded the module. After that the field was still in model res.partner. Even after I deleted the field in pgsql database, the field was still there in the model.

Is this normal? How to remove a field in such case?