Fix tests using FixedSizeArray methods (which are now shadowed)

library/core/tests/lib.rs

@@ -1,5 +1,6 @@
 #![feature(alloc_layout_extra)]
 #![feature(array_chunks)]
+#![feature(array_methods)]
 #![feature(array_map)]
 #![feature(bool_to_option)]
 #![feature(bound_cloned)]

library/core/tests/option.rs

@@ -1,4 +1,3 @@
-use core::array::FixedSizeArray;
 use core::clone::Clone;
 use core::mem;
 use core::ops::DerefMut;

library/core/tests/result.rs

@@ -1,4 +1,3 @@
-use core::array::FixedSizeArray;
 use core::ops::DerefMut;
 use core::option::*;