Remove deprecated unstable alloc::heap::EMPTY constant

Author: SimonSapin

src/liballoc/heap.rs

@@ -228,14 +228,6 @@ unsafe impl Alloc for Heap {
     }
 }
 
-/// An arbitrary non-null address to represent zero-size allocations.
-///
-/// This preserves the non-null invariant for types like `Box<T>`. The address
-/// may overlap with non-zero-size memory allocations.
-#[rustc_deprecated(since = "1.19.0", reason = "Use Unique/NonNull::empty() instead")]
-#[unstable(feature = "heap_api", issue = "27700")]
-pub const EMPTY: *mut () = 1 as *mut ();
-
 /// The allocator for unique pointers.
 // This function must not unwind. If it does, MIR trans will fail.
 #[cfg(not(test))]