Use generic sinf/cosf in lgammaf_r

Use generic sinf/cosf in lgammaf_r

The internal functions __kernel_sinf and __kernel_cosf are used only by
lgammaf_r.  Removing the internal functions and using the generic sinf
and cosf is better overall.  Benchmarking on Cortex-A72 shows the generic
sinf and cosf are 1.4x and 2.3x faster in the range |x| < PI/4, and 0.66x
and 1.1x for |x| < PI/2, so it should make lgammaf_r faster on average.

GLIBC regression tests pass on AArch64.

	* sysdeps/ieee754/flt-32/e_lgammaf_r.c (sin_pif): Use __sinf/__cosf.
	* sysdeps/ieee754/flt-32/k_cosf.c (__kernel_cosf): Remove all code.
	* sysdeps/ieee754/flt-32/k_sinf.c (__kernel_sinf): Likewise.