system/cu: remove canonical input mode from termios flag

ASCII_DEL will unable to handle after below change:
apache/nuttx#14037

| commit df5c876932c4c82e8aee32adca651bb99d9d6200
| Author: zhangwenjian <[email protected]>
| Date:   Thu May 23 13:13:48 2024 +0800
|
|     libc:getline support backspace
|
|     Signed-off-by: zhangwenjian <[email protected]>

remove canonical input mode to support backspace in cu

Signed-off-by: chao an <[email protected]>

Author: anchao

system/cu/cu_main.c

@@ -194,7 +194,7 @@ static int set_termios(FAR struct cu_globals_s *cu, int nocrlf)
 
       tio.c_iflag = 0;
       tio.c_oflag = 0;
-      tio.c_lflag &= ~ECHO;
+      tio.c_lflag &= ~(ECHO | ICANON);
 
       ret = tcsetattr(cu->stdfd, TCSANOW, &tio);
       if (ret)