x86-64: Remove s_sincosf-sse2.S

The current s_sincosf.c is faster than s_sincosf-sse2.S.  On Broadwell
with FMA disabled, bench-sincosf shows:

       Before         After      Improvement
max    154.032        114.517        34%
min    6.25           5.609          11%
mean   14.8728        12.8589        15%

	* sysdeps/x86_64/fpu/s_sincosf.S: Removed.
	* sysdeps/x86_64/fpu/multiarch/s_sincosf-sse2.S: Likewise.
	* sysdeps/x86_64/fpu/multiarch/s_sincosf-sse2.c: New file.