Remove (filter out) reactions with disease xrefs

[dustine32]

There are some reactions in non-disease pathways that have DOID xrefs. These reactions should be filtered out of the final GO-CAM.

Example: Reaction R-HSA-9761900 in pathway R-HSA-9755511 - DOID:2043

This DOID is a RelationshipXref on the Reaction in BioPAX. Checking for any DOID RelationshipXref on a reaction should be a good enough rule to code.