vt: keyboard, remove ctrl_alt_del declaration

ctrl_alt_del is already declared in linux/reboot.h which we include. So
remove this second (superfluous) declaration.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Link: https://lore.kernel.org/r/20201029113222.32640-1-jslaby@suse.cz
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/vt/keyboard.c

@@ -49,8 +49,6 @@
 
 #include <asm/irq_regs.h>
 
-extern void ctrl_alt_del(void);
-
 /*
  * Exported functions/variables
  */