fdutimens, fdutimensat: update signature, again

fdutimens, fdutimensat: update signature, again

In general, merging:

f<act>(fd,args) and <act>at(dir,name,args)

should produce:

fd<act>at(fd,dir,name,args)

* lib/utimens.h (gl_futimens): Delete, and move signature...
(fdutimens): ...here.
(fdutimensat): Rearrange signature.
(lutimensat): Rename variable for clarity.
* lib/fdutimensat.c (fdutimensat): Update signature.
* lib/utimens.c (fdutimens): Likewise.
(gl_futimens): Delete.
(utimens, lutimens): Update callers.
* lib/futimens.c (futimens): Likewise.
* tests/test-fdutimensat.c: Likewise.
* tests/test-utimens.c: Likewise.
* tests/test-futimens.h: Update comment.
* NEWS: Mention this.
Suggested by Paul Eggert.

Signed-off-by: Eric Blake <eblake@redhat.com>