sparc64: Kill __ARCH_WANT_UNLOCKED_CTXSW

As Peter Z. explained at:

https://lkml.org/lkml/2011/12/12/268

it's not needed at all and I even tested it back then.
This patch just got lost in the shuffle for some reason.
Reported-by: NKirill Tkhai <tkhai@yandex.ru>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

arch/sparc/include/asm/processor_64.h

@@ -18,9 +18,6 @@
 #include <asm/ptrace.h>
 #include <asm/page.h>
 
-/* Don't hold the runqueue lock over context switch */
-#define __ARCH_WANT_UNLOCKED_CTXSW
-
 /* The sparc has no problems with write protection */
 #define wp_works_ok 1
 #define wp_works_ok__is_a_macro /* for versions in ksyms.c */