Update hex-literal version, simplify imports and remove unused dependencies (#2371)

substrate/subkey/Cargo.toml

@@ -16,7 +16,7 @@ rustc-hex = "2.0"
 substrate-bip39 = { git = "https://github.com/paritytech/substrate-bip39" }
 schnorrkel = "0.1"
 hex = "0.3"
-hex-literal = "0.1"
+hex-literal = "0.2"
 parity-codec = "3.2"
 
 [features]

substrate/subkey/src/main.rs

@@ -18,11 +18,8 @@
 #[cfg(feature = "bench")]
 extern crate test;
 
-extern crate substrate_bip39;
-extern crate rustc_hex;
-#[macro_use] extern crate hex_literal;
-
 use std::io::{stdin, Read};
+use hex_literal::hex;
 use clap::load_yaml;
 use rand::{RngCore, rngs::OsRng};
 use substrate_bip39::mini_secret_from_entropy;