Remove shlib-versions ABI names support.

Remove shlib-versions ABI names support.

shlib-versions files can contain ABI lines that map triplets to a
canonical ABI name.  This name was once used for various purposes
where test baseline files for different ABIs went in a single
directory; now these purposes use sysdeps files, generation of headers
which have per-ABI variants uses abi-variants and related Makefile
variables and the shlib-versions ABI names are unused.  This patch
duly removes those lines and associated build system support for them.

Tested for x86_64 (both a full testsuite run and confirming the
installed shared libraries are unchanged by the patch).

	* Makeconfig ($(common-objpfx)soversions.mk): Do not generate
	abi-name definition.
	* scripts/soversions.awk: Do not handle or generate ABI lines.
	* shlib-versions: Remove ABI entries.
	* sysdeps/powerpc/nofpu/shlib-versions: Remove file.
	* sysdeps/x86_64/x32/shlib-versions: Remove ABI entry.