Hide feedback opportunity message

## Describe the bug

For every `az` command that I run, I get the following message displayed:

```
Please let us know how we are doing: https://aka.ms/azureclihats
and let us know if you're interested in trying out our newest features: https://aka.ms/CLIUXstudy
```

Is there a way to disable this message?

## To reproduce

Run any `az` command, for example `az --help`.

## Expected behavior

This message is shown alongside information that describes how to disable the message.

## Environment summary
```
Windows-10-10.0.18362-SP0
Python 3.6.8
Installer: MSI

azure-cli 2.21.0

Extensions:
application-insights 0.1.13
```