Remove powerpc bits/mathinline.h.

Continuing the process of moving away from having bits/mathinline.h
headers in glibc, leaving the compiler to inline functions as
appropriate depending on the options passed to it, this patch removes
the header for powerpc.
<https://gcc.gnu.org/bugzilla/show_bug.cgi?id=88558> is the
corresponding GCC bug for adding replacements for these powerpc
(32-bit-only) lrint / lrintf inlines.

Tested with build-many-glibcs.py for its powerpc configurations.

	* sysdeps/powerpc/bits/mathinline.h: Remove.