Remove XPCOM component interface.

According to the [MDN documentation][1], declaring an XPCOM interface isn't actually required for services that will only be accessed from Javascript - which is the case for the Greasemonkey service. This PR thus removes the interface (the compiled xpt seems to have been outdated anyway, since it wasn't updated in 62dd079f75d0c6759df79db26c96838600b678c7).

[1]: https://developer.mozilla.org/en-US/docs/How_to_Build_an_XPCOM_Component_in_Javascript#Using_wrappedJSObject