Convert artist.el to lexical binding

Convert artist.el to lexical binding

* lisp/textmodes/artist.el (artist-system, (artist-flood-fill):
Remove binding of the obsolete variables binary-process-input,
binary-process-output and input-queue.
(artist-down-mouse-1): Fix mistyped 'echo-keystrokes'; bind it to 0.
(artist-fill-rect, artist-fill-square, artist-pen-set-arrow-points)
(artist-spray-clear-circle, artist-spray-set-radius)
(artist-draw-ellipse-with-0-height, artist-fill-ellipse)
(artist-ff-is-topmost-line, artist-ff-is-bottommost-line)
(artist-set-arrow-points-for-2points, artist-key-undraw-continously)
(artist-key-undraw-poly, artist-key-undraw-1point)
(artist-key-undraw-2points, artist-key-do-continously-1point)
(artist-key-set-point-1point, artist-shift-has-changed)
(artist-mouse-draw-continously, artist-mouse-draw-1point)
(artist-submit-bug-report): Suppress warnings about unused parameters
which are there for function signature commonality.  Remove unused
variables.