Touch up where `Alloc` is imported from

src/destructors.md

@@ -26,15 +26,11 @@ this is totally fine.
 For instance, a custom implementation of `Box` might write `Drop` like this:
 
 ```rust
-#![feature(alloc, heap_api, unique, allocator_api)]
+#![feature(unique, allocator_api)]
 
-extern crate alloc;
+use std::heap::{Heap, Alloc, Layout};
-
-use std::ptr::{drop_in_place, Unique};
 use std::mem;
-
+use std::ptr::{drop_in_place, Unique};
-use alloc::allocator::{Layout, Alloc};
-use alloc::heap::Heap;
 
 struct Box<T>{ ptr: Unique<T> }
 
@@ -56,16 +52,12 @@ use-after-free the `ptr` because when drop exits, it becomes inaccessible.
 However this wouldn't work:
 
 ```rust
-#![feature(alloc, allocator_api, heap_api, unique)]
+#![feature(allocator_api, unique)]
-
-extern crate alloc;
 
+use std::heap::{Heap, Alloc, Layout};
 use std::ptr::{drop_in_place, Unique};
 use std::mem;
 
-use alloc::allocator::{Layout, Alloc};
-use alloc::heap::Heap;
-
 struct Box<T>{ ptr: Unique<T> }
 
 impl<T> Drop for Box<T> {
@@ -131,16 +123,12 @@ The classic safe solution to overriding recursive drop and allowing moving out
 of Self during `drop` is to use an Option:
 
 ```rust
-#![feature(alloc, allocator_api, heap_api, unique)]
+#![feature(allocator_api, unique)]
-
-extern crate alloc;
 
+use std::heap::{Alloc, Heap, Layout};
 use std::ptr::{drop_in_place, Unique};
 use std::mem;
 
-use alloc::allocator::{Layout, Alloc};
-use alloc::heap::Heap;
-
 struct Box<T>{ ptr: Unique<T> }
 
 impl<T> Drop for Box<T> {

src/vec-final.md

@@ -2,17 +2,13 @@
 
 ```rust
 #![feature(unique)]
-#![feature(alloc, allocator_api, heap_api)]
+#![feature(allocator_api)]
-
-extern crate alloc;
 
 use std::ptr::{Unique, self};
 use std::mem;
 use std::ops::{Deref, DerefMut};
 use std::marker::PhantomData;
-
+use std::heap::{Alloc, Layout, Heap};
-use alloc::allocator::{Layout, Alloc};
-use alloc::heap::Heap;
 
 struct RawVec<T> {
     ptr: Unique<T>,
@@ -64,16 +60,13 @@ impl<T> Drop for RawVec<T> {
         let elem_size = mem::size_of::<T>();
         if self.cap != 0 && elem_size != 0 {
             unsafe {
-                Heap.dealloc(self.ptr.as_ptr() as *mut _, Layout::array::<T>(self.cap).unwrap());
+                Heap.dealloc(self.ptr.as_ptr() as *mut _,
+                             Layout::array::<T>(self.cap).unwrap());
             }
         }
     }
 }
 
-
-
-
-
 pub struct Vec<T> {
     buf: RawVec<T>,
     len: usize,