remove_shadow() - remove all shadows from the specified object, or remove
a specified shadow from another object. does not destruct the shadow.


int remove_shadow(object ob);


ob defaults to this_object()
returns 0 if object is either destroyed or is no shadow and isn't shadowed
returns 1 otherwise

ob <- shadow1 <- shadow2

remove(shadow2): ob <- shadow1 shadow2
remove(shadow1): ob <- shadow2 shadow1
remove(ob): shadow1 <- shadow2 ob

#ifndef NO_SHADOWS