api: never include non-data fields in json export (#87918)

tests/api/test_formdata.py

@@ -163,6 +163,7 @@ def test_formdata(pub, local_user, user, auth):
     block = BlockDef()
     block.name = 'foobar'
     block.fields = [
+        fields.TitleField(id='dsd', label='Title'),
         fields.StringField(id='abc', label='Foo', varname='foo'),
         fields.ItemField(id='xyz', label='Test', data_source={'type': 'foobar'}, varname='bar'),
     ]

wcs/formdata.py

@@ -1488,6 +1488,8 @@ class FormData(StorableObject):
         for field in fields:
             if anonymise and field.anonymise == 'final':
                 continue
+            if field.is_no_data_field:
+                continue
             if not field.varname and not include_unnamed_fields:
                 continue
             if field.varname in seen: