Revert "Update /drush dir for Drush9"

This reverts commit 902fa86.

Author: weitzman

drush/Commands/PolicyCommands.php

@@ -0,0 +1,38 @@
+<?php
+
+/*
+ * Customize this file as desired. See https://github.com/drush-ops/drush/blob/8.x/examples/policy.drush.inc for documentation.
+ */
+
+/**
+ * Implements drush_hook_COMMAND_validate().
+ *
+ * Encourage folks to use `composer` instead of Drush pm commands
+ */
+function drush_policy_pm_updatecode_validate() {
+  return _deny_message();
+}
+
+function drush_policy_pm_update_validate() {
+  return _deny_message();
+}
+
+function drush_policy_pm_download_validate() {
+  return _deny_message();
+}
+
+function _deny_message() {
+  if (!drush_get_option('pm-force')) {
+    $msg = 'This codebase is assembled with Composer instead of Drush. Use `composer update` and `composer require` instead of `drush pm-updatecode` and `drush pm-download`. You may override this error by using the --pm-force option.';
+    return drush_set_error('POLICY_PM_DENY', dt($msg));
+  }
+}
+
+/**
+ * Implements hook_drush_help_alter().
+ */
+function policy_drush_help_alter(&$command) {
+  if (in_array($command['command'], array('pm-updatecode', 'pm-update', 'pm-download'))) {
+    $command['options']['pm-force'] = 'Override site policy and allow Drush codebase management (pm-* commands)';
+  }
+}