Since FuncTypes are represented as structs rather than linking the
parameter lists together, we no longer need to worry about duplicating
the parameter lists.

Change-Id: I3767aa3cd1cbeddfb80a6eef6b42290dc2ac14ae
Reviewed-on: https://go-review.googlesource.com/28574
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>