I suggest you update the module 'base' before you try Benjamin's solution.

I have updated 'base' module and it didn't help me, I also updated all modules and it didn't help me. Didn't try Benjamin's solution yet.

So here is how it works for me:

After restarting Odoo server those fields that I deleted from the model and view didn't fell out. I checked my db and they were still there. Then I uninstalled my module. I went to Accounting module where I was customizing "res.partner" form and I didn't see those fields that I deleted earlier, which is what I expected, but I was still able to see other custom fields that I didn't delete from the model and view even after I uninstalled the whole module. So then I updated the Accounting module and only after that those other custom fields that I saw earlier where gone (actually later I just refreshed a browser and fields were gone).

However, at this point I went and checked my db. Those custom fields that I didn't delete from the model/view fall out from the db, but those fields that I deleted from the model/view were still there. So if I understand everything right then if I want to delete my custom fields from the db I need to:

1) uninstall my module;

2) refresh browser;

3) delete unnecessary custom fields from the model and view;

4) install my module back without those unnecessary fields.

So when I go to settings/database structure/fields and search for my custom fields Odoo doesn't show them to me anymore, which is what I expected.