Auto merge of #10706 - zwn:unused-extern-crates, r=nox

Turn on unused-extern-crates warning.

As discussed in #9256. It should solve second half of the issue.

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components/util/lib.rs

@@ -18,6 +18,7 @@
 #![deny(unsafe_code)]
 
 extern crate app_units;
+#[allow(unused_extern_crates)]
 #[macro_use]
 extern crate bitflags;
 extern crate deque;
@@ -27,6 +28,7 @@ extern crate heapsize;
 extern crate ipc_channel;
 #[cfg(feature = "non-geckolib")]
 extern crate js;
+#[allow(unused_extern_crates)]
 #[macro_use]
 extern crate lazy_static;
 extern crate libc;

components/util/resource_files.rs

@@ -2,6 +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/. */
 
+#[cfg(not(target_os = "android"))]
 use std::env;
 use std::fs::File;
 use std::io::{self, Read};