Don't call purecopy in vc/*.el

Don't call purecopy in vc/*.el

* lisp/vc/diff.el (diff-command, diff-switches):
* lisp/vc/ediff-hook.el (menu-bar-ediff-misc-menu)
(menu-bar-epatch-menu, menu-bar-ediff-merge-menu)
(menu-bar-ediff-menu):
* lisp/vc/pcvs-defs.el (cvs-global-menu):
* lisp/vc/vc-hooks.el (vc-menu-entry)
(vc-directory-exclusion-list):
* lisp/vc/vc-rcs.el (vc-rcs-master-templates):
* lisp/vc/vc-sccs.el (vc-sccs-master-templates):
* lisp/vc/vc-src.el (vc-src-master-templates): Remove calls to purecopy.

(cherry picked from commit 8bd246d87ea9cf02cab0a229e89b1648e9462c2e)