cmd: drop cork command

This SDK is not used anymore

Signed-off-by: Mathieu Tortuyaux <mtortuyaux@microsoft.com>

Author: tormath1

README.md

@@ -17,7 +17,6 @@ locally or in a cloud.
 
 ## Overview
 Mantle is composed of many utilities:
- - `cork` for handling the Container Linux SDK
  - `kola` for launching instances and running tests
  - `kolet` an agent for kola that runs on instances
  - `ore` for interfacing with cloud providers
@@ -28,11 +27,6 @@ and options.
 
 ## Tools
 
-### cork
-Cork is a now-deprecated tool that was used to help in working with Container Linux images and the SDK.
-
-Please see [developer guides](https://www.flatcar.org/docs/latest/reference/developer-guides/) to see how to work with Flatcar SDK.
-
 ### kola
 Kola is a framework for testing software integration in Container Linux instances
 across multiple platforms. It is primarily designed to operate within