Remove parameter annotation

[Valouleloup]

There is no sense to let this annotation if we accept classes that implement InstantiatorInterface with a parameter different than string

[alcaeus]

This is a major BC break for very similar reasons as in #44. I'm closing this as it makes no sense from my point of view, and to consolidate discussion around this in #44.

Even though we don't do scalar types yet, implementations of the interface rely on the docblock to provide implementation guidance and thus only expect string arguments.