Remove special time handling

diff --git a/aleksis/apps/chronos/schema/__init__.py b/aleksis/apps/chronos/schema/__init__.py
index 2790034..e89f225 100644
--- a/aleksis/apps/chronos/schema/__init__.py
+++ b/aleksis/apps/chronos/schema/__init__.py
@@ -80,7 +80,7 @@ class DatetimeTimezoneMixin:
         return value

-class AmendLessonBatchCreateMutation(DatetimeTimezoneMixin, BaseBatchCreateMutation):
+class AmendLessonBatchCreateMutation(BaseBatchCreateMutation):
     class Meta:
         model = LessonEvent
         permissions = ("chronos.edit_substitution_rule",)
@@ -104,7 +104,7 @@ class AmendLessonBatchCreateMutation(DatetimeTimezoneMixin, BaseBatchCreateMutat
         return created_objects

-class AmendLessonBatchPatchMutation(DatetimeTimezoneMixin, BaseBatchPatchMutation):
+class AmendLessonBatchPatchMutation(BaseBatchPatchMutation):
     class Meta:
         model = LessonEvent
         permissions = ("chronos.edit_substitution_rule",)