**Apache Airflow version**: 2.1.0

**Browsers**: Chrome and Firefox

**What happened**:

Before upgrading to 2.1.0

![before](https://user-images.githubusercontent.com/14293802/120359517-c1ca1100-c2d5-11eb-95ba-58ccc0a3ac37.png)

After upgrading to 2.1.0

![after](https://user-images.githubusercontent.com/14293802/120359528-c4c50180-c2d5-11eb-8e04-f34846ea2736.png)

**What you expected to happen**:

Show/Edit/Delete under Security -> Users are available

<!-- What do you think went wrong? -->

**How to reproduce it**:

Go to Security -> Users (as an admin of course) 
airflow/www/views.py
return redirect(url_for('Airflow.index'))
        xcomlist = (
            session.query(XCom)
            .filter(XCom.dag_id == dag_id, XCom.task_id == task_id, XCom.execution_date == dttm)
            .all()
        )
        attributes = []
        for xcom in xcomlist:
            if not xcom.key.startswith('_'):
                attributes.append((xcom.key, xcom.value))
        title = "XCom"
        return self.render_template(
            'airflow/xcom.html',
            attributes=attributes,
            task_id=task_id,
            execution_date=execution_date,
            form=form,
            root=root,
            dag=dag,
            title=title,
        )
    @expose('/run', methods=['POST'])
    @auth.has_access(
        [
            (permissions.ACTION_CAN_READ, permissions.RESOURCE_DAG),
            (permissions.ACTION_CAN_CREATE, permissions.RESOURCE_TASK_INSTANCE),
        ]
    )
    @action_logging
    def run(self):