Remove pre-Django 4.2 fallback code from JSONField null handling migration

wagtail/migrations/0089_log_entry_data_json_null_to_object.py

@@ -1,6 +1,5 @@
 # Generated by Django 4.2.3 on 2023-07-31 11:00
 
-from django import VERSION as DJANGO_VERSION
 from django.db import migrations, models
 
 
@@ -8,12 +7,7 @@ def replace_json_null_with_empty_object(apps, schema_editor):
     ModelLogEntry = apps.get_model("wagtailcore.ModelLogEntry")
     PageLogEntry = apps.get_model("wagtailcore.PageLogEntry")
 
-    # https://github.com/django/django/pull/16245
-    # The way to express a JSON `null` value was changed in Django 4.2.
-    if DJANGO_VERSION >= (4, 2):
-        null = models.Value(None, models.JSONField())
-    else:
-        null = models.Value("null")
+    null = models.Value(None, models.JSONField())
 
     ModelLogEntry.objects.filter(data=null).update(data={})
     PageLogEntry.objects.filter(data=null).update(data={})