Fix lint errors

Author: Stjepan Glavina

src/liballoc/lib.rs

@@ -83,7 +83,6 @@
 #![cfg_attr(not(test), feature(core_float))]
 #![cfg_attr(not(test), feature(exact_size_is_empty))]
 #![cfg_attr(not(test), feature(slice_rotate))]
-#![cfg_attr(not(test), feature(sort_unstable))]
 #![cfg_attr(not(test), feature(str_checked_slicing))]
 #![cfg_attr(test, feature(rand, test))]
 #![feature(allocator)]