Stop sending or processing the origin field in PDUs (#18418)

Co-authored-by: Quentin Gliech <quenting@element.io>
Co-authored-by: Eric Eastwood <erice@element.io>

contrib/graph/graph.py

@@ -45,6 +45,10 @@ def make_graph(pdus: List[dict], filename_prefix: str) -> None:
     colors = {"red", "green", "blue", "yellow", "purple"}
 
     for pdu in pdus:
+        # TODO: The "origin" field has since been removed from events generated
+        # by Synapse. We should consider removing it here as well but since this
+        # is part of `contrib/`, it is left for the community to revise and ensure things
+        # still work correctly.
         origins.add(pdu.get("origin"))
 
     color_map = {color: color for color in colors if color in origins}