Replace local intersection functions with seq-intersection

Replace local intersection functions with seq-intersection

* lisp/doc-view.el (doc-view-intersection):
* lisp/gnus/gnus-range.el (gnus-intersection):
* lisp/htmlfontify.el (hfy-interq):
* lisp/loadhist.el (file-set-intersect):
* lisp/mail/smtpmail.el (smtpmail-intersection): Make obsolete in
favor of seq-intersection.  Update all callers.

* lisp/url/url-dav.el (url-intersection): Redefine as obsolete
function alias for seq-intersection.  Update callers.

* lisp/mpc.el (mpc-intersection, mpc-cmd-list, mpc-reorder):
Use seq-intersection.