Fix UAF in comps_objmrtree_unite function

The added field is not used at all in many places and it is probably the
left-over of some copy-paste.
void comps_rtree_set_n(COMPS_RTree * rt, char * key, size_t keylen, void * data)
{
    __comps_rtree_set(rt, key, keylen, data);
}

void comps_rtree_set_n(COMPS_RTree * rt, char * key, size_t keylen, void * data)
{
    __comps_rtree_set(rt, key, keylen, data);
}
