Move dired-guess commands from dired-x to dired

Move dired-guess commands from dired-x to dired

* lisp/dired-x.el (dired-shell-command-history)
(dired-guess-shell-alist-default, dired-guess-default)
(dired-guess-shell-command): Move from here...
* lisp/dired-aux.el (dired-shell-command-history)
(dired-guess-shell-alist-default, dired-guess-default)
(dired-guess-shell-command): ...to here.  (Bug#21981)

* lisp/dired-x.el (dired-guess-shell-gnutar)
(dired-guess-shell-gzip-quiet, dired-guess-shell-znew-switches)
(dired-guess-shell-case-fold-search, dired-guess-shell-alist-user):
Move from here...
* lisp/dired.el (dired-guess-shell-gnutar)
(dired-guess-shell-gzip-quiet, dired-guess-shell-znew-switches)
(dired-guess-shell-case-fold-search, dired-guess-shell-alist-user):
...to here.  Change :group to dired-guess.
(dired-guess): New defgroup.

* test/lisp/dired-x-tests.el (dired-guess-default): Move from here...
* test/lisp/dired-aux-tests.el (dired-guess-default): ...to here.

* doc/misc/dired-x.texi (Features, Technical Details, Installation):
Delete any mention of shell command guessing.
(Shell Command Guessing): Move from here...
* doc/emacs/dired.texi (Shell Command Guessing): ...to here.  Adapt to
better fit the Emacs Manual conventions.
* lisp/dired-aux.el (dired-do-shell-command): Doc fix to adjust for
above changes.
* etc/NEWS: Announce the above change.