Instead of the added complexity of discarding flow nodes
we can simplify the compilation process by just retaining
them and jumping over them in further iteration and graph
and tree runtime usage.
This change moves toward a model that does just this, which
makes it also easier to in the future use the newly added
flow graph nodes to do meaningful things (like use them as
a point to change which flow_detail is used).
Change-Id: Icb1695f4b995a0392f940837514774768f222db4