obj.Linksymfmt is no longer referenced by any packages in cmd/...

Change-Id: Id4d9213d1577e13580b60755dbf7da313b17cb0e
Reviewed-on: https://go-review.googlesource.com/41171
Run-TryBot: Dave Cheney <dave@cheney.net>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>