Remove shlib-versions entries redundant with DEFAULT entries.

Remove shlib-versions entries redundant with DEFAULT entries.

When a shlib-versions file has a DEFAULT line, it's not necessary to
specify the same default minimum symbol version on the lines for
individual libraries.  If those lines otherwise duplicate the default
SONAME for the library in question, they can be removed completely.

This patch makes such cleanups: version entries for ld.so are removed
(leaving just the definition of the architecture-specific dynamic
linker name) and entries for libpthread are removed completely (since
the default is libpthread.so.0).

Tested for x86_64 that the installed shared libraries are unchanged by
this patch.

There are various architectures (hppa, ia64, mips, sh, sparc64) that
define minimum symbol versions (or in the case of mips, omission of
symbol versions) only for particular libraries without a DEFAULT line.
None of these are equivalent to something simpler with a DEFAULT line
because all have some other libraries, not explicitly mentioned, with
symbol versions that would be omitted were such a line used.  In the
mips case I'm pretty sure it was a mistake not to omit the 2.1 symbols
for libthread_db; for the others I don't know if it was a mistake or
deliberate that some symbols in various libraries have 2.0 or 2.1
versions despite other libraries having a 2.2 minimum.

This concludes the shlib-versions cleanups I'm aware of.

	* sysdeps/unix/sysv/linux/powerpc/powerpc64/shlib-versions: Do not
	specify symbol version for ld.so.  Do not include entry for
	libpthread.
	* sysdeps/unix/sysv/linux/s390/s390-64/shlib-versions: Likewise.
	* sysdeps/unix/sysv/linux/x86_64/64/shlib-versions: Likewise.
	* sysdeps/unix/sysv/linux/x86_64/x32/shlib-versions: Likewise.