Remove __ARM_HAVE_HALFWORD_MULTIPLY.

Bug: 18556103
Change-Id: I17e498539f77ddf7d1fb980ee93155d3c3ccd85e
diff --git a/libc/arch-arm/include/machine/cpu-features.h b/libc/arch-arm/include/machine/cpu-features.h
index 0725c74..ef62010 100644
--- a/libc/arch-arm/include/machine/cpu-features.h
+++ b/libc/arch-arm/include/machine/cpu-features.h
@@ -53,11 +53,6 @@
 #  endif
 #endif
 
-/* define __ARM_HAVE_HALFWORD_MULTIPLY when half-word multiply instructions
- * this means variants of: smul, smulw, smla, smlaw, smlal
- */
-#define  __ARM_HAVE_HALFWORD_MULTIPLY  1
-
 /* define _ARM_HAVE_VFP if we have VFPv3
  */
 #if __ARM_ARCH__ >= 7 && defined __VFP_FP__