Don't mention linuxthreads in Depend files.

I noticed that some of the Depend files, used to determine the
subdirectory build order in sysd-sorted, still mentioned linuxthreads,
although it hasn't been supported for many years.  This patch removes
those references.  In the case of nscd, it substitutes an nptl
reference, since I believe there is a fact a thread library dependence
there; the others already mentioned nptl.

Note that I am not at all confident in the completeness of these
Depend files.

Note also that references to linuxthreads remain in a comment in
sysdeps/unix/sysv/linux/ia64/Versions, and in manual/maint.texi,
manual/signal.texi and scripts/documented.sh.

Tested x86_64 that the installed shared libraries are unchanged by the
patch (as is sysd-sorted).

	* nscd/Depend (linuxthreads): Remove.
	(nptl): Add.
	* resolv/Depend (linuxthreads): Remove.
	* rt/Depend (linuxthreads): Remove.

rt/Depend

@@ -1,2 +1 @@
-linuxthreads
 nptl