Remove vmss identity message

### **This is autogenerated. Please review and update as needed.**

## Describe the bug
The message suggesting the customer has to manually update instances is incorrect, and should be removed. Since identity is tracked at the VMSS level, customer does not need to update individual instances

fisteele@caroldanvers:/mnt/c/Users/fisteele$ az vmss identity assign -n uniformtest -g demorg
_With manual upgrade mode, you will need to run 'az vmss update-instances -g demorg -n uniformtest --instance-ids *' to propagate the change_
{
"systemAssignedIdentity": "c179f17b-02c3-428b-80c2-0e5eb6fb5bab",
"userAssignedIdentities": {}
}

**Command Name**
`az vmss identity assign`

**Errors:**
```

```

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

- _Put any pre-requisite steps here..._
- `az vmss identity assign -n {} -g {}`

## Expected Behavior

## Environment Summary
```
Linux-5.10.60.1-microsoft-standard-WSL2-x86_64-with-debian-buster-sid
Python 3.6.10
Installer: DEB

azure-cli 2.27.1

Extensions:
interactive 0.4.5
ssh 0.1.5

```
## Additional Context