third_party/README.md content is deprecated

[chai2010]

Bug Report

Please answer these questions before submitting your issue. Thanks!

1. Minimal reproduce step (Required)

https://github.com/KusionStack/kusion/blob/main/third_party/README.md

File content is deprecated, Grumpy is not used in any code

2. What did you expect to see? (Required)

3. What did you see instead (Required)

4. What is your KusionStack components version? (Required)