sparc64: drop unused SLOW_DOWN_IO definitions

They are no longer used.
All hits in the kernel are essential unused code or comments

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

arch/sparc/include/asm/io_64.h

@@ -9,10 +9,6 @@
 #include <asm/asi.h>
 #include <asm-generic/pci_iomap.h>
 
-/* PC crapola... */
-#define __SLOW_DOWN_IO	do { } while (0)
-#define SLOW_DOWN_IO	do { } while (0)
-
 /* BIO layer definitions. */
 extern unsigned long kern_base, kern_size;