vsdg: remove jive_node_isinstance
vsdg: remove jive_node_isinstance

All instance checks are now done on the operations embedded in nodes.

Signed-off-by: Nico Reißmann <d8255cca0642bdc1e6f9b45da9cb618d308e389b@gmail.com>

phate/jive,phate/jive,phate/jive