Extraneous/unused types: psoa and nom-obj

[emilymbender]

While documenting, I found two types that I think aren't used:

psoa := mrs &
[ HOOK.INDEX event ]
"""Type listed for deletion""".

nom-obj := mrs &
[ HOOK.INDEX index ]
"""Type listed for deletion""".

Remove & test that nothing breaks. When removing, remove associated comment or consider relocating it to other types.