since builds is_many should specify as array

While Workflow might support passing singular items into is_many inputs
it is better if the thing that has knowledege about the inputs (the
model) specifies a list with one element.  Flow does not wrap single
elements in a list.
it seems like default implies optional but it doesn't so make explicit

This fixes what looks like an invalid workflow due to missing inputs
since the inputs have default values but aren't marked as optional.
remove unused line