(stable) Remove the "ssh-auth-key" script

Summary:
Ref T13436. Historically, this script could be used with a forked copy of "sshd" to do lower-cost per-key auth.

Relatively modern "sshd" supports "%f" to "AuthorizedKeysCommand", which effectively moots this.

Users have never been instructed to use this script for anything, and we moved away from this specific patch to "sshd" some time ago.

Test Plan: Grepped for "ssh-auth-key", no hits.

Maniphest Tasks: T13436

Differential Revision: https://secure.phabricator.com/D20873

bin/ssh-auth-key

@@ -1 +0,0 @@
-../scripts/ssh/ssh-auth-key.php

scripts/ssh/ssh-auth-key.php

@@ -1,42 +0,0 @@
-#!/usr/bin/env php
-<?php
-
-$root = dirname(dirname(dirname(__FILE__)));
-require_once $root.'/scripts/__init_script__.php';
-
-try {
-  $cert = file_get_contents('php://stdin');
-  $public_key = PhabricatorAuthSSHPublicKey::newFromRawKey($cert);
-} catch (Exception $ex) {
-  exit(1);
-}
-
-$key = id(new PhabricatorAuthSSHKeyQuery())
-  ->setViewer(PhabricatorUser::getOmnipotentUser())
-  ->withKeys(array($public_key))
-  ->withIsActive(true)
-  ->executeOne();
-if (!$key) {
-  exit(1);
-}
-
-$object = $key->getObject();
-if (!($object instanceof PhabricatorUser)) {
-  exit(1);
-}
-
-$bin = $root.'/bin/ssh-exec';
-$cmd = csprintf('%s --phabricator-ssh-user %s', $bin, $object->getUsername());
-// This is additional escaping for the SSH 'command="..."' string.
-$cmd = addcslashes($cmd, '"\\');
-
-$options = array(
-  'command="'.$cmd.'"',
-  'no-port-forwarding',
-  'no-X11-forwarding',
-  'no-agent-forwarding',
-  'no-pty',
-);
-
-echo implode(',', $options);
-exit(0);