Memory leak when deleting object metadata

[denisvmedyantsev]

It is assumed that when an object is deleted, all metadata associated with it is also deleted. Now, it is necessary to delete attributes separately, or the amount of memory occupied by the application will increase.

pseudocode

        for obj_meta in frame_meta.objects:
            nvds_remove_obj_attrs(frame_meta.frame_meta, obj.object_meta_impl.ds_object_meta)  # this line shouldn't be necessary
            frame_meta.remove_obj_meta(obj)

[bwsw]

Backport to Savant 0.4.