Remove AUTHORS.txt and add-authors.sh

Keeping this file up to date requires hours of work every release,
even with the script. It is a fool's errand and we shall not do it
any longer.

src/etc/add-authors.sh

-#!/bin/sh
-
-# Copyright 2014 The Rust Project Developers. See the COPYRIGHT
-# file at the top-level directory of this distribution and at
-# http://rust-lang.org/COPYRIGHT.
-#
-# Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
-# http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
-# <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
-# option. This file may not be copied, modified, or distributed
-# except according to those terms.
-
-# This script, invoked e.g. "add-authors.sh 1.0.0..rust-lang/master",
-# will merge new authors into AUTHORS.txt, obeying the mailmap
-# file.
-#
-# After running this script, run `git diff` to manually inspect
-# changes. If there are incorrect additions fix it by editing
-# .mailmap and re-running the script.
-
-if [ "${1-}" = "" ]; then
-    echo "Usage: add-authors.sh 1.0.0..rust-lang/master"
-    exit 1
-fi
-
-set -u -e
-
-range="$1"
-
-authors_file="./AUTHORS.txt"
-tmp_file="./AUTHORS.txt.tmp"
-old_authors="$(cat "$authors_file" | tail -n +2 | sed "/^$/d" | sort)"
-new_authors="$(git log "$range" --use-mailmap --format="%aN <%aE>" | sort | uniq)"
-
-printf "%s\n\n" "Rust was written by these fine people:" > "$tmp_file"
-printf "%s\n%s" "$old_authors" "$new_authors" | sort -fs | uniq >> "$tmp_file"
-mv -f "$tmp_file" "$authors_file"