Use directory-files-no-dot-files-regexp wherever possible

Use directory-files-no-dot-files-regexp wherever possible

Suggested by Paul Eggert.

* lisp/files.el (directory-files-no-dot-files-regexp):
Clarify semantics and purpose.
* lisp/dired.el (dired-re-no-dot):
Define as obsolete alias of directory-files-no-dot-files-regexp.
(dired-delete-file):
* lisp/gnus/gnus-util.el (gnus-delete-directory):
* lisp/net/ange-ftp.el (ange-ftp-delete-directory):
* lisp/obsolete/vc-arch.el (vc-arch-trim-revlib):
* lisp/org/ob-core.el (org-babel-remove-temporary-directory):
* lisp/vc/vc-rcs.el (vc-rcs-unregister):
Use directory-files-no-dot-files-regexp.