Log Message:
(Editors/emacs26) Default options adjustment, drop ImageMagick and set gtk3.

1. ImageMagick is listed as buildlink3, but configure stage says no.
   Drop from the default options for now. (need py-wand and ImageMagick 6 ?)
2. gtk/gtk3 logic was not the same as emacs-25.x. Default was gtk2.
   Now default is gtk3 (the same as emacs-25). Option gtk and gtk2
   have the same effect now.

Thanks tsutsui@ for information