**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
"""Customize permission names for FAB's builtin RoleModelView."""
    class_permission_name = permissions.RESOURCE_ROLE
    method_permission_name = {
        'delete': 'delete',
        'download': 'read',
        'show': 'read',
        'list': 'read',
        'edit': 'edit',
        'add': 'create',
        'copy_role': 'create',
    }
    base_permissions = [
        permissions.ACTION_CAN_CREATE,
        permissions.ACTION_CAN_READ,
        permissions.ACTION_CAN_EDIT,
        permissions.ACTION_CAN_DELETE,
    ]
class CustomViewMenuModelView(ViewMenuModelView):
    """Customize permission names for FAB's builtin ViewMenuModelView."""
    class_permission_name = permissions.RESOURCE_VIEW_MENU
    method_permission_name = {
        'list': 'read',
    }
    base_permissions = [
        permissions.ACTION_CAN_READ,
    ]
class CustomUserDBModelView(UserDBModelView):