**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
running_task_instance_query_result = session.query(
            TaskInstance.dag_id.label('dag_id'), TaskInstance.state.label('state')
        ).join(
            running_dag_run_query_result,
            and_(
                running_dag_run_query_result.c.dag_id == TaskInstance.dag_id,
                running_dag_run_query_result.c.execution_date == TaskInstance.execution_date,
            ),
        )
        if conf.getboolean('webserver', 'SHOW_RECENT_STATS_FOR_COMPLETED_RUNS', fallback=True):
            last_dag_run = (
                session.query(DagRun.dag_id, sqla.func.max(DagRun.execution_date).label('execution_date'))
                .join(DagModel, DagModel.dag_id == DagRun.dag_id)
                .filter(DagRun.state != State.RUNNING, DagModel.is_active)
                .group_by(DagRun.dag_id)
            )
            last_dag_run = last_dag_run.filter(DagRun.dag_id.in_(filter_dag_ids))
            last_dag_run = last_dag_run.subquery('last_dag_run')
            
            
            last_task_instance_query_result = session.query(
                TaskInstance.dag_id.label('dag_id'), TaskInstance.state.label('state')
            ).join(
                last_dag_run,
                and_(
                    last_dag_run.c.dag_id == TaskInstance.dag_id,
                    last_dag_run.c.execution_date == TaskInstance.execution_date,
                ),
            )
            final_task_instance_query_result = union_all(