Remove uses of using() from migrations

This hardcoded the db_alias fetched from schema_editor and forces django
to try and migrate any second database you use, rather than routing to
the default database.  In testing a build from scratch, these do not
appear needed.

Using using() prevents us from using multiple databases behind edxapp

milestones/migrations/0002_data__seed_relationship_types.py

@@ -9,9 +9,8 @@ from milestones.data import fetch_milestone_relationship_types
 def seed_relationship_types(apps, schema_editor):
     """Seed the relationship types."""
     MilestoneRelationshipType = apps.get_model("milestones", "MilestoneRelationshipType")
-    db_alias = schema_editor.connection.alias
     for name in fetch_milestone_relationship_types().values():
-        MilestoneRelationshipType.objects.using(db_alias).get_or_create(
+        MilestoneRelationshipType.objects.get_or_create(
             name=name,
             description='Autogenerated milestone relationship type "{}"'.format(name),
         )
@@ -20,9 +19,8 @@ def seed_relationship_types(apps, schema_editor):
 def delete_relationship_types(apps, schema_editor):
     """Clean up any relationships we made."""
     MilestoneRelationshipType = apps.get_model("milestones", "MilestoneRelationshipType")
-    db_alias = schema_editor.connection.alias
     for name in fetch_milestone_relationship_types().values():
-        MilestoneRelationshipType.objects.using(db_alias).filter(name=name).delete()
+        MilestoneRelationshipType.objects.filter(name=name).delete()
 
 
 class Migration(migrations.Migration):