Merge 'Va neuron' and 'ventral group vA neuron'

[Clare72]

Similar descriptions and both express Capa, but need to check refs

[Clare72]

Both FBrf0201188 (ref for 'Va neuron') and FBrf0214309 (ref for 'ventral group vA') reference FBrf0146873 (Kean et al., 2002) when referring to VA neurons and there seem to be a limited number of capability neurons, so these terms seem to be equivalent.

There is some disagreement about which abdominal segments they are in (first 3 vs A2-4), but a more recent paper (Gabilondo et al., 2018 - FBrf0238644) confirms the A2-A4 designation, saying that the A1 neurons express DH31 and AstA, rather than Capa (might be FBbt:00053261).

The two Va neuron terms should be merged (and perhaps renamed to reflect Capa expression).