Move script lints to script_plugins

The plugins crate now just allows to hook into clippy from a single crate.

tests/compiletest/plugin/compile-fail/trustedpromise_mustnot_deriveclone.rs

@@ -2,9 +2,6 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
-#![feature(plugin)]
-#![plugin(plugins)]
-
 extern crate script;
 
 use script::test::TrustedPromise;