cmd/newlink: delete

cmd/newlink: delete

cmd/link is clearly the way forward.
The original rationale for cmd/newlink was that it would be a clean Go reimplementation.
But when push came to shove, cmd/link got converted from C instead,
and all the work on build modes and the like is in cmd/link now.
Cleaning up cmd/link is likely a much better plan.

This directory is something to delete from releases and the
testdata is something that breaks every time the .6 format changes.
Fix both problems by just deleting it outright.

Change-Id: Ib00fecda258ba685f1752725971182af9d4459eb
Reviewed-on: https://go-review.googlesource.com/20380
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>