Remove edge correlations in decode_detection_events_for_up_to_64_observables

[smadhuk]

See https://github.com/oscarhiggott/PyMatching/pull/134/files/588606173bca458cab23cb8673a5027483a4ccd2#r2247518912

[oscarhiggott]

I think maybe we should close this, as it's fine to keep the option for correlations here as long as it defaults to false.