When compiling a package that defines a type T with method T.M, we
already compile and emit the wrapper method (*T).M. There's no need
for every package that uses T to do the same.

Change-Id: I3ca2659029907570f8b98d66111686435fad7ed0
Reviewed-on: https://go-review.googlesource.com/74412
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: David Crawshaw <crawshaw@golang.org>