s_sincosl.c: remove unused variable

Newer versions of clang complain about this, and it seems genuinely unneeded.

It was in the original commit, and judging from that I think it's just
a copy & paste leftover from inlinine sinl() and cosl() --- the <
M_PI_4 case in sinl() needs the original sign.

(I've cc:ed the original author.)

diff --git a/lib/msun/src/s_sincosl.c b/lib/msun/src/s_sincosl.c
index aef36c2320b..3dd34575f89 100644
--- a/lib/msun/src/s_sincosl.c
+++ b/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();