alpha: remove unused __SLOW_DOWN_IO and SLOW_DOWN_IO definitions

Remove unused __SLOW_DOWN_IO and SLOW_DOWN_IO definitions.
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Signed-off-by: Matt Turner <mattst88@gmail.com>

arch/alpha/include/asm/io.h

@@ -14,10 +14,6 @@
    the implementation we have here matches that interface.  */
 #include <asm-generic/iomap.h>
 
-/* We don't use IO slowdowns on the Alpha, but.. */
-#define __SLOW_DOWN_IO	do { } while (0)
-#define SLOW_DOWN_IO	do { } while (0)
-
 /*
  * Virtual -> physical identity mapping starts at this offset
  */