Clean up hierarchy immediately under neuron

[dosumis]

If it is a grouping class:

• Is It needed?
• Is classification under it complete?
• Is classification under it sustainable. Can we realistically populate classes - ideally with inferred classification. If yes - document required work on a new ticket
• Is it well defined - textually and logically?

If it is not a grouping class:

• What taxonomic groupings does it apply to (can we add taxon restriction?) - useful to be able to separate out mammalian neuronal types from others.
• Is it well defined - textually and logically - in this case this probably means having on necessary conditions for class membership, i.e. subclassof axioms but no EquivalentClass axioms
• Can we axiomatise it so that it is no longer at the top level?

  ### Tasks
  - [ ] https://github.com/obophenotype/cell-ontology/issues/2428
  - [ ] https://github.com/obophenotype/cell-ontology/issues/2357

[AvolaAmg]

Not immediately under neuron, this is under interneuron, but it is a class hierarchy related to neurons #2357 .