Fix up some unnecessary uses of unsafe.

components/script/parse/html.rs

@@ -2,7 +2,7 @@
  * 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/. */
 
-#![allow(unsafe_code, unrooted_must_root)]
+#![allow(unrooted_must_root)]
 
 use document_loader::DocumentLoader;
 use dom::bindings::codegen::Bindings::DocumentBinding::DocumentMethods;