Fix amends field of LessonEvent in gql schema

aleksis/apps/chronos/schema/__init__.py

@@ -35,15 +35,6 @@ class TimetableRoomType(DjangoObjectType):
         skip_registry = True
 
 
-# There is another unrelated CalendarEventType in aleksis/core/schema/calendar
-# This CalendarEventType is needed for the inherited amends field of LessonEvent
-# to work in the graphql query.
-class CalendarEventForLessonEventType(DjangoObjectType):
-    class Meta:
-        model = CalendarEvent
-        fields = ("id", "amends", "datetime_start", "datetime_end")
-
-
 class LessonEventType(DjangoObjectType):
     class Meta:
         model = LessonEvent
@@ -63,6 +54,8 @@ class LessonEventType(DjangoObjectType):
             "id": ["exact", "lte", "gte"],
         }
 
+    amends = graphene.Field(lambda: LessonEventType, required=False)
+
 
 class DatetimeTimezoneMixin:
     """Handle datetimes for mutations with CalendarEvent objects.