Add code to disentangle downstream events when the active unit is the same in two different reactions

[vanaukenk]

From the 2023-10-12 Reactome2GO meeting at NYU:

In the nuclear signaling by ERBB4 model, regulation of GFAP and S100b are an example of this situation.

[dustine32]

The red arrows below show how the two causally_upstream_of edges should really be connected:

[ukemi]

@dustine32 discovered this is a data issue at source. The upstream reaction in Reactome is incorrect and needs to be changed to the S100B-gene binding and not the GFAP gene binding.

[deustp01]

The upstream reaction in Reactome is incorrect

now fixed