Diversion: Remove error "The downstream node of a Diversion node must be different than the downstream node of the node is attached to"

I don't know why I've imposed this constraint in the first place.

This kind of network scheme makes sense and can be handled by the model:

graph LR

id_54032[54032]

id_54001[54001]

id_54029[54029]

id_54001[54001]

id_54001 -->| 45 km| id_54032

id_54029 -->| 32 km| id_54032

id_54001 -->| 60 km| id_54032

class id_54032 IntermediateGauged

class id_54001,id_54001 UpstreamGaugedDiversion

class id_54029 UpstreamUngauged

classDef default stroke:#333

classDef UpstreamUngauged fill:#eef

classDef UpstreamGauged fill:#aaf

classDef IntermediateUngauged fill:#efe

classDef IntermediateGauged fill:#afa

classDef DirectInjection fill:#faa

classDef Reservoir fill:#9de

classDef UpstreamUngaugedDiversion fill:#eef, stroke:#faa, stroke-width:3px

classDef UpstreamGaugedDiversion fill:#aaf, stroke:#faa, stroke-width:3px

classDef IntermediateUngaugedDiversion fill:#efe, stroke:#faa, stroke-width:3px

classDef IntermediateGaugedDiversion fill:#afa, stroke:#faa, stroke-width:3px

linkStyle 2 stroke:#faa, stroke-width:2px,stroke-dasharray: 5 5;