session: remove unused dependency

src/net/session.rs

@@ -2,7 +2,6 @@ use std::cmp;
 use std::collections::{BTreeMap, HashMap};
 use std::fs::File;
 use std::io::{Seek, SeekFrom, Write};
-use std::net::{Shutdown, TcpStream};
 use std::os::unix::io::AsRawFd;
 use std::sync::Arc;
 use std::sync::mpsc::{self, Receiver, Sender};