Revert "Allow custom fields in the Device CSV form"

This reverts commit 07a7fac.
We've now migrated to Netbox and we don't need anymore this local
change and it's easier to upgrade the repository to the latest upstream
version without local modifications.

The upstream issue for this is:
netbox-community/netbox#568

Bug: T205896
Change-Id: Id71e0e2ed1e817d18bb5c67575e294625b266c8b

Author: volans-

netbox/dcim/forms.py

@@ -825,7 +825,7 @@ def __init__(self, *args, **kwargs):
             self.initial['rack'] = self.instance.parent_bay.device.rack_id
 
 
-class BaseDeviceCSVForm(BootstrapMixin, CustomFieldForm):
+class BaseDeviceCSVForm(forms.ModelForm):
     device_role = forms.ModelChoiceField(
         queryset=DeviceRole.objects.all(),
         to_field_name='name',

netbox/utilities/templatetags/helpers.py

@@ -116,7 +116,7 @@ def example_choices(field, arg=3):
         if not id:
             continue
         examples.append(label)
-    return ', '.join([ str(e) for e in examples ]) or 'None'
+    return ', '.join(examples) or 'None'
 
 
 #