package.json will always use 2 spaces

According to https://github.com/npm/npm/pull/3180#issuecomment-16336516 the `package.json` file will always use 2 spaces. This must be reflected in the `.editorconfig` file.
I agree about the comments being unnecessary, but I think the indent_style = space should stay. We've indeed already specified the indent_style but it's under the Change these settings to your own preference section.