Cleanup liballoc use statements

Some modules were still using the deprecated `allocator` module, use the
`alloc` module instead.

Some modules were using `super` while it's not needed.

Some modules were more or less ordering them, and other not, so the
latter have been modified to match the others.

src/liballoc/vec.rs

@@ -82,11 +82,11 @@ use core::ptr;
 use core::ptr::NonNull;
 use core::slice;
 
+use alloc::CollectionAllocErr;
 use borrow::ToOwned;
 use borrow::Cow;
 use boxed::Box;
 use raw_vec::RawVec;
-use super::allocator::CollectionAllocErr;
 
 /// A contiguous growable array type, written `Vec<T>` but pronounced 'vector'.
 ///