Fix slash stripping in Image data migration

arkindex/images/migrations/0003_stripslashes_data.py

@@ -16,7 +16,7 @@ def deduplicate_and_strip(apps, schema_editor):
             ImageServer.objects.annotate(
                 # PostgreSQL supports trimming things that are not just spaces,
                 # But django.db.models.functions.Trim doesn't.
-                trimmed_url=RawSQL("trim(trailing '/' from url)", ())
+                trimmed_url=RawSQL("trim(leading '/' from url)", ())
             ).order_by('trimmed_url'),
             key=lambda s: s.trimmed_url,
         )