New File/Project Dialog: Don't use &c twice

I'm not sure how the cancel button gets that accelerator, but the
default button should not have a accelarator anyway.

Task-number: QTCREATORBUG-10608
Change-Id: I18899bfa039a82f0cbb2cf6ae0ed21a9f0e619d8
Reviewed-by: Eike Ziller <eike.ziller@digia.com>