feeder: remove json_field of formdef cubes (fixes #28936)

wcs_olap/feeder.py

@@ -796,6 +796,8 @@ class WcsFormdefFeeder(object):
 
         # create cube
         cube = self.cube = copy.deepcopy(self.base_cube)
+        # remove json field from formdef cubes
+        cube.pop('json_field', None)
         cube.update({
             'name': self.table_name,
             'label': self.formdef.schema.name,