Collection remove the redundant mainItem model attr.

django_etesync/migrations/0039_remove_collection_mainitem.py

@@ -0,0 +1,17 @@
+# Generated by Django 3.0.3 on 2020-04-16 08:28
+
+from django.db import migrations
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('django_etesync', '0038_remove_collectionitemrevision_chunks'),
+    ]
+
+    operations = [
+        migrations.RemoveField(
+            model_name='collection',
+            name='mainItem',
+        ),
+    ]