az keyvault purge without arguments gives invalid help output

## Describe the bug

**Command Name**
`az keyvault purge`

**Errors:**
```
Please specify --vault-name or --hsm-name.
```

## To Reproduce:
Steps to reproduce the behavior. Note that argument values have been redacted, as they may contain sensitive information.

- `az keyvault purge

This gives the output as above, indicating that `--vault-name` is a valid argument.

## Expected Behavior

Error should read:

```
Please specify --name or --hsm-name.
```

## Environment Summary
```
Windows-10-10.0.19041-SP0
Python 3.6.8
Installer: MSI

azure-cli 2.22.1

Extensions:
aks-preview 0.4.72
databricks 0.7.0
interactive 0.4.4

```
## Additional Context