It looks like I misunderstood what the original rules meant and all content of
all `.vscode` directory should be ignored, but for the `.vscode/extensions.json`
and `.vscode/tasks.json` files. Since these file are already tracked, they don't
need a dedicated ignore rules. However other files does (e.g
`.vscode/settings.json`, `.vscode/launch.json`, etc).

So we remove the exception for the root `.vscode` directory.

This is a follow up to 4952395ba0ec.

Differential Revision: https://phabricator.services.mozilla.com/D209260