Simplify builder implementation with AmpForm-DPD v0.2

[redeboer]

Since AmpForm-DPD v0.2.0, final state particles carry an index (State class). This makes it possible to simplify/generalize code like this

polarimetry/src/polarimetry/lhcb/__init__.py

Lines 182 to 189 in 77a2a18

	if resonance.name.startswith("K"):
	child1, child2, spectator = π, K, p
	elif resonance.name.startswith("L"):
	child1, child2, spectator = K, p, π
	elif resonance.name.startswith("D"):
	child1, child2, spectator = p, π, K
	else:
	raise NotImplementedError