Deleted workspace roles can be used in 'Department Management'

Created by: wenxin-01

Versions used(KubeSphere/Kubernetes) KubeSphere: ks3.1

Preset conditions There is a workspace role 'test-role' in workspace 'test'

To Reproduce Steps to reproduce the behavior:

1. Go to workspace 'test'
2. Click on 'Workspace Settings'
3. Click on 'Department Management'
4. Click on 'Set Department'
5. Create a department named 'test-group' use workspace role 'test-role'
6. Delete workspace role 'test-role'
7. Go to 'Set Department ' check department 'test-group' and click on 'ok'

Expected behavior When deleting a role, it indicates that the role has been used by the department, and can not delete

Actual behavior

https://user-images.githubusercontent.com/68640256/117752097-c7898500-b248-11eb-8432-c9c3e782c502.mov

/kind bug /priority low /milestone 3.1.0 /assign @xuliwenwenwen