src/sage/plot/plot3d/base.pyx: no native Windows paths

We're dropping Cygwin support, and in particular, the pycygwin library
that handles these paths.

Author: orlitzky

src/sage/plot/plot3d/base.pyx

@@ -285,13 +285,8 @@ cdef class Graphics3d(SageObject):
             tachyon.png.save_as(preview_png)
         else:
             # Java needs absolute paths
-            # On cygwin, they should be native ones
             scene_native = scene_zip
 
-            if sys.platform == 'cygwin':
-                import cygwin
-                scene_native = cygwin.cygpath(scene_native, 'w')
-
             script = '''set defaultdirectory "{0}"\nscript SCRIPT\n'''.format(scene_native)
             jdata.export_image(targetfile=preview_png, datafile=script,
                                image_type="PNG",