Uninstalling the extension does not appear to work, starting somewhere around the August 2021 vscode release.
It relied on vscode deleting the actual extension files instead of marking them in:

C:\Users\<user>\.vscode\extensions\.obsolete

Removing them from Sumneko's external libraries path does not seem possible when uninstalling, since we don't have access to the vscode api in the uninstall hook.

• Provide access to VS Code API in extension uninstall lifecycle hook microsoft/vscode#45474
• https://github.com/sumneko/lua-language-server/wiki/EmmyLua-Libraries