Don't call purecopy in help-mode.el

Don't call purecopy in help-mode.el

* lisp/help-mode.el (help-function, help-variable, help-type)
(help-face, help-coding-system, help-input-method)
(help-character-set, help-symbol, help-back, help-forward)
(help-info-variable, help-info, help-man)
(help-customization-group, help-url, help-customize-variable)
(help-customize-face, help-function-def, help-function-cmacro)
(help-variable-def, help-face-def, help-package)
(help-package-def, help-theme-def, help-theme-edit)
(help-dir-local-var-def, help-news, help-back-label)
(help-forward-label, help-xref-symbol-regexp)
(help-xref-info-regexp, help-xref-man-regexp)
(help-xref-customization-group-regexp, help-xref-url-regexp):
Remove calls to purecopy.

(cherry picked from commit 065b6f2fa7a75fda446dc755edfee555b6e6d704)