* lisp/textmodes/ispell.el (ispell-look-p): Make obsolete.
(ispell-lookup-words): Look up the look command at run time
instead (bug#50852).
(ispell-have-new-look): Make obsolete.
(ispell-look-options): Adjust. Apparently the version of "look"
that had a "-r" (regexp interface) never took off -- it's not
present in GNU/Linux or Macos, at least, as far as we can tell.