Forgotten stuff in nu-pretty-hex

Seems to be prehistoric for a potential `no_std` use. That part has been
commented out already so bye bye

crates/nu-pretty-hex/src/lib.rs

@@ -1,5 +1,3 @@
-// #![no_std]
-
 //! A Rust library providing pretty hex dump.
 //!
 //! A `simple_hex()` way renders one-line hex dump, and a `pretty_hex()` way renders
@@ -59,8 +57,5 @@
 //! 0018:   db b1 bc 35 bf ee         ...5..
 //! ```
 
-#[cfg(feature = "alloc")]
-extern crate alloc;
-
 mod pretty_hex;
 pub use pretty_hex::*;