nptl: Remove longjmp, siglongjmp from libpthread

The definitions in libc are sufficient, the forwarders are no longer
needed.

The symbols have been moved using scripts/move-symbol-to-libc.py.
s390-linux-gnu and s390x-linux-gnu need a new version placeholder
to keep the GLIBC_2.19 symbol version in libpthread.

Tested on i386-linux-gnu, powerpc64le-linux-gnu, s390x-linux-gnu,
x86_64-linux-gnu.  Built with build-many-glibcs.py.

Reviewed-by: Adhemerval Zanella <adhemerval.zanella@linaro.org>