powerpc: Remove ununsed s_float_bitwise.h

This file is not used anywhere since removal of {k,e}_rem_pio2f.c
(commit ca3aac57).

Checked with a build for powerpc-linux-gnu (with --with-cpu=power4
and --with-cpu=power7), powerpc64-linux-gnu (with --with-cpu=power4
and --with-cpu=power7), and powerpc64le-linux (with --with-cpu=power8).

	* sysdeps/powerpc/fpu/s_float_bitwise.h: Remove file.