Deny unsafe code in some more modules.

components/style/selector_matching.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/. */
 
-// For lazy_static
-#![allow(unsafe_code)]
-
 use dom::PresentationalHintsSynthetizer;
 use element_state::*;
 use error_reporting::StdoutErrorReporter;