**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
for task in dag.tasks:
            y_points = []
            x_points = []
            for ti in tis:
                dttm = wwwutils.epoch(ti.execution_date)
                x_points.append(dttm)
                
                y_points.append(ti.prev_attempted_tries)
            if x_points:
                chart.add_serie(name=task.task_id, x=x_points, y=y_points)
        tries = sorted({ti.try_number for ti in tis})
        max_date = max(ti.execution_date for ti in tis) if tries else None
        chart.create_y_axis('yAxis', format='.02f', custom_format=False, label='Tries')
        chart.axislist['yAxis']['axisLabelDistance'] = '-15'
        session.commit()
        form = DateTimeWithNumRunsForm(
            data={
                'base_date': max_date or timezone.utcnow(),
                'num_runs': num_runs,
            }
        )
        chart.buildcontent()
        return self.render_template(
            'airflow/chart.html',
            dag=dag,
            root=root,
            form=form,
            chart=Markup(chart.htmlcontent),
            tab_title='Tries',
        )