configure.ac: fix: do not define HAVE_NEON unconditionally

Change-Id: I761a7afaeda9d232ac26edff47949e911f8f1f0c
diff --git a/configure.ac b/configure.ac
index cc8d3a7..d249be9 100644
--- a/configure.ac
+++ b/configure.ac
@@ -384,8 +384,6 @@
 		[Enable ARM NEON instructions support [default=no]]
 	)],
 	[neon=$enableval], [neon="no"])
-AC_DEFINE(HAVE_NEON,,
-[Support ARM NEON instructions])
 AM_CONDITIONAL(HAVE_NEON, [test "x$neon" != "xno"])