Remove unused imports from the UART implementation

src/basic_uart.rs

@@ -1,5 +1,5 @@
 use std::collections::VecDeque;
-use std::io::{Read, Write, stdin, stdout};
+use std::io::{Read, stdin};
 use std::sync::{Arc, Mutex};
 use std::thread;
 use std::time::Duration;