auto merge of #13183 : erickt/rust/remove-list, r=alexcrichton

`collections::list::List` was decided in a [team meeting](https://github.com/mozilla/rust/wiki/Meeting-weekly-2014-03-25) that it was unnecessary, so this PR removes it. Additionally, it removes an old and redundant purity test and fixes some warnings.

src/libstd/unstable/mutex.rs

@@ -621,7 +621,7 @@ mod test {
     #[test]
     fn destroy_immediately() {
         unsafe {
-            let mut m = StaticNativeMutex::new();
+            let m = StaticNativeMutex::new();
             m.destroy();
         }
     }