microblaze: kill incorrect __bad_xchg definition

The whole point of the __bad_xchg declaration in
system.h is to give a linker error when a variable
of invalid size is passed to __xchg. The out
of line definition in traps.c defeats this purpose
and does not any value, so remove it here.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Michal Simek <monstr@monstr.eu>

arch/microblaze/kernel/traps.c

@@ -22,14 +22,6 @@ void trap_init(void)
 	__enable_hw_exceptions();
 }
 
-void __bad_xchg(volatile void *ptr, int size)
-{
-	printk(KERN_INFO "xchg: bad data size: pc 0x%p, ptr 0x%p, size %d\n",
-		__builtin_return_address(0), ptr, size);
-	BUG();
-}
-EXPORT_SYMBOL(__bad_xchg);
-
 static int kstack_depth_to_print = 24;
 
 static int __init kstack_setup(char *s)