Remove unused extern statement

extern crate keywords are no longer needed to import a crate

bitcoin/examples/bip32.rs

@@ -1,5 +1,3 @@
-extern crate bitcoin;
-
 use std::{env, process};
 
 use bitcoin::address::{Address, KnownHrp};

bitcoin/examples/handshake.rs

@@ -1,5 +1,3 @@
-extern crate bitcoin;
-
 use std::io::{BufReader, Write};
 use std::net::{IpAddr, Ipv4Addr, Shutdown, SocketAddr, TcpStream};
 use std::time::{SystemTime, UNIX_EPOCH};