In reproductive routing table, "from" should be unique

[mnlevy1981]

There are some assert statements in other parts of the code that force some linking types to have unique indices; that should be matched in the reproduction_routing type

[matt-long]

See example in food_web:

feisty/feisty/core/ecosystem.py

Line 404 in 860c93a

assert len(set(pred_prey)) == len(pred_prey), 'non-unique predator-prey relationships'

However, I think we want each parent to appear only once and each child to appear only once.