Evas: Replace image_map_surface_free by common image_free

Evas: Replace image_map_surface_free by common image_free

Those two functions were doing exactly the same thing[1], which
is free an image, so this commit only attempts to simplify the code
a little bit.

[1] Actually image_map_surface_free() might even not have worked
properly with cserve2 sw (calling unload instead of close).