cmd/go: remove script and script.txt

Fixes #9824.

Change-Id: Id318c61b6884e4fd294f7b0946dcc306f746ee0a
Reviewed-on: https://go-review.googlesource.com/4891Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/cmd/go/script

-#!/bin/sh
-
-x() {
-	echo '--- ' "$@"
-	"$@"
-	echo '---'
-	echo
-}
-
-x go help
-x go help build
-x go help clean
-x go help install
-x go help fix
-x go help fmt
-x go help get
-x go help list
-x go help test
-x go help version
-x go help vet
-x go help gopath
-x go help importpath
-x go help remote