Remove set-but-unused variable from s_sincosl.c

This look like a copy and paste leftover.

Reported by:	enh@google.com (via freebsd-numerics@)
Reviewed by:	Steve Kargl <sgk@troutmask.apl.washington.edu>
MFC after:	3 days

lib/msun/src/s_sincosl.c

@@ -50,11 +50,10 @@ void
 sincosl(long double x, long double *sn, long double *cs)
 {
 	union IEEEl2bits z;
-	int e0, sgn;
+	int e0;
 	long double y[2];
 
 	z.e = x;
-	sgn = z.bits.sign;
 	z.bits.sign = 0;
 
 	ENTERV();