Undo the use of #include <...> because it caused some errors.

drivers/tty/tty.c

@@ -71,8 +71,6 @@
 #include <sys/time.h>
 #include <sys/select.h>
 
-extern int irq_hook_id;
-
 unsigned long kbd_irq_set = 0;
 unsigned long rs_irq_set = 0;
 

drivers/tty/tty.h

@@ -106,7 +106,6 @@ typedef struct tty {
 /* Memory allocated in tty.c, so extern here. */
 extern tty_t tty_table[NR_CONS+NR_RS_LINES+NR_PTYS];
 extern int ccurrent;		/* currently visible console */
-extern int irq_hook_id;		/* hook id for keyboard irq */
 extern u32_t system_hz;		/* system clock frequency */
 
 extern unsigned long kbd_irq_set;