Remove Typesafe copyright line pending clarification.

This line was added under the belief that this was simply a clarification of existing agreements.

I still think it's the right thing to do for the Scala project
(my understanding is that it doesn't give Typesafe any rights not already provided by the license itself;
it's purely an attribution and a legal defense mechanism in case someone challenges the copyright).

Nonetheless, I agree we should not add it until everyone is convinced it's the right thing to do.