Add _req_user to removed item so you can use this in the remove pre/p…

…ost hook

As discussed in keystonejs/keystone#1857 the remove pre/post hooks are "missing" the _req_user. I, amongst others, am using this object to handle some permissions. It's available in the updateHandler (in `create` and `update`) but missing in `remove`.

it's added on the updateHandler here: https://github.com/keystonejs/keystone/blob/d34f45662eb359e2cb18b397f2ffea21f9883141/lib/list/updateItem.js#L157

Remove doesn't use the updateHandler, so this is missing.

admin/server/api/list/delete.js

@@ -38,6 +38,7 @@ module.exports = function (req, res) {
 			return res.apiError('database error', err);
 		}
 		async.forEachLimit(results, 10, function (item, next) {
+			item._req_user = req.user;
 			item.remove(function (err) {
 				if (err) return next(err);
 				deletedCount++;