locking/refcounts: Remove stale comment from the ARCH_HAS_REFCOUNT Kconfig entry

ARCH_HAS_REFCOUNT is no longer marked as broken ('if BROKEN'), so remove
the stale comment regarding it being broken.
Signed-off-by: Eric Biggers <ebiggers@google.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20171229195303.17781-1-ebiggers3@gmail.comSigned-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/Kconfig

@@ -55,7 +55,6 @@ config X86
 	select ARCH_HAS_GCOV_PROFILE_ALL
 	select ARCH_HAS_KCOV			if X86_64
 	select ARCH_HAS_PMEM_API		if X86_64
-	# Causing hangs/crashes, see the commit that added this change for details.
 	select ARCH_HAS_REFCOUNT
 	select ARCH_HAS_UACCESS_FLUSHCACHE	if X86_64
 	select ARCH_HAS_SET_MEMORY