Remove some ineffectual calls to purecopy

Remove some ineffectual calls to purecopy

* lisp/dired.el (dired-chown-program, dired-trivial-filenames):
* lisp/emacs-lisp/shortdoc.el (shortdoc--display-function):
* lisp/help-fns.el (help-fns--mention-shortdoc-groups):
* lisp/mail/mail-extr.el (mail-extr-full-name-prefixes)
(mail-extr-all-letters-but-separators, mail-extr-all-letters)
(mail-extr-first-letters, mail-extr-last-letters)
(mail-extr-bad-dot-pattern, mail-extr-full-name-suffix-pattern)
(mail-extr-alternative-address-pattern)
(mail-extr-trailing-comment-start-pattern)
(mail-extr-name-pattern, mail-extr-telephone-extension-pattern)
(mail-extr-ham-call-sign-pattern, mail-extr-normal-name-pattern)
(mail-extr-two-name-pattern)
(mail-extr-listserv-list-name-pattern)
(mail-extr-stupid-vms-date-stamp-pattern)
(mail-extr-hz-embedded-gb-encoded-chinese-pattern)
(mail-extr-x400-encoded-address-pattern)
(mail-extr-x400-encoded-address-field-pattern-format)
(mail-extr-x400-encoded-address-surname-pattern)
(mail-extr-x400-encoded-address-given-name-pattern)
(mail-extr-x400-encoded-address-full-name-pattern): Remove
ineffectual calls to purecopy.