openrisc/traps: Remove die_if_kernel function

This was noticed when I saw this warning:

    arch/openrisc/kernel/traps.c:234:6: warning: no previous prototype for 'die_if_kernel' [-Wmissing-prototypes]
      234 | void die_if_kernel(const char *str, struct pt_regs *regs, long err)
	  |      ^~~~~~~~~~~~~

The die_if_kernel function is not used in the OpenRISC port so remove
it.

Signed-off-by: Stafford Horne <shorne@gmail.com>

arch/openrisc/kernel/traps.c

@@ -235,15 +235,6 @@ void __noreturn die(const char *str, struct pt_regs *regs, long err)
 	make_task_dead(SIGSEGV);
 }
 
-/* This is normally the 'Oops' routine */
-void die_if_kernel(const char *str, struct pt_regs *regs, long err)
-{
-	if (user_mode(regs))
-		return;
-
-	die(str, regs, err);
-}
-
 void unhandled_exception(struct pt_regs *regs, int ea, int vector)
 {
 	printk("Unable to handle exception at EA =0x%x, vector 0x%x",