Remove cursor-changed callback from canvases (fix #848)
Remove cursor-changed callback from canvases (fix #848)

- removes the cursor-changed callback from canvases. It only works correctly
  as coded when invoked from a viewer.

naojsoft/ginga,naojsoft/ginga,ejeschke/ginga,pllim/ginga,ejeschke/ginga,naojsoft/ginga,pllim/ginga,ejeschke/ginga,pllim/ginga