Remove #![feature(const_raw_ptr_deref)]

It's now stable in nightly.

Author: yvt

README.md

@@ -61,5 +61,5 @@ features = ["unstable_const"]
 
 Your crate root: (`lib.rs`/`main.rs`)
 ```rust,ignore
-#![feature(const_ptr_offset_from, const_raw_ptr_deref, const_refs_to_cell)]
+#![feature(const_ptr_offset_from, const_refs_to_cell)]
 ```

src/lib.rs

@@ -58,7 +58,7 @@
 #![no_std]
 #![cfg_attr(
     feature = "unstable_const",
-    feature(const_ptr_offset_from, const_raw_ptr_deref, const_refs_to_cell)
+    feature(const_ptr_offset_from, const_refs_to_cell)
 )]
 
 #[macro_use]