Fix some warnings in ptyd

ptyd/src/pgrp.rs

@@ -1,6 +1,5 @@
 use std::cell::RefCell;
 use std::rc::Weak;
-use std::{mem, slice};
 
 use syscall::error::{Error, Result, EBADF, EINVAL, EPIPE};
 use syscall::flag::{EventFlags, F_GETFL, F_SETFL, O_ACCMODE};

ptyd/src/pty.rs

@@ -3,7 +3,7 @@ use std::io::{Cursor, Write};
 
 use redox_termios::*;
 use syscall;
-use syscall::error::{Error, Result, ENAMETOOLONG};
+use syscall::error::Result;
 
 pub struct Pty {
     pub id: usize,