Can't uninstall extensions

[golf1052]

When you try to uninstall an extension it gets reinstalled by CodeSync. I'm assuming because it's not picking up the correct list of actually installed extensions when exporting the extensions list.

[golf1052]

Fully fixing this is blocked by microsoft/vscode#14444

Documented a workaround in the README here: https://github.com/golf1052/code-sync#uninstalling-extensions

[golf1052]

This is now fixed in 1.31 because the extension list updates when extensions are added, removed, enabled or disabled. However disabled extensions will not be exported.