unix: delete asm.s

This contains a stub for func "use", which was deleted.

See issue https://golang.org/issue/16607

Change-Id: I7165ca55ad956ac449e950f2be6f53cfeb8e6ffa
Reviewed-on: https://go-review.googlesource.com/36720Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

unix/asm.s

-// Copyright 2014 The Go Authors.  All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file.
-
-// +build !gccgo
-
-#include "textflag.h"
-
-TEXT ·use(SB),NOSPLIT,$0
-	RET