replace user_schema with serialize method on user model

this is so that we can filter out inactive organisations and services

note: can't remove user schema completely, as we still use it in
POST /user to create new users

app/organisation/rest.py

@@ -20,7 +20,6 @@ from app.organisation.organisation_schema import (
     post_link_service_to_organisation_schema,
 )
 from app.schema_validation import validate
-from app.schemas import user_schema
 
 organisation_blueprint = Blueprint('organisation', __name__)
 register_errors(organisation_blueprint)
@@ -98,15 +97,13 @@ def get_organisation_services(organisation_id):
 @organisation_blueprint.route('/<uuid:organisation_id>/users/<uuid:user_id>', methods=['POST'])
 def add_user_to_organisation(organisation_id, user_id):
     new_org_user = dao_add_user_to_organisation(organisation_id, user_id)
-    return jsonify(data=user_schema.dump(new_org_user).data), 200
+    return jsonify(data=new_org_user.serialize())
 
 
 @organisation_blueprint.route('/<uuid:organisation_id>/users', methods=['GET'])
 def get_organisation_users(organisation_id):
     org_users = dao_get_users_for_organisation(organisation_id)
-
-    result = user_schema.dump(org_users, many=True)
-    return jsonify(data=result.data)
+    return jsonify(data=[x.serialize() for x in org_users])
 
 
 @organisation_blueprint.route('/unique', methods=["GET"])