Remove DagNode.__hash__()

[levbishop]

Defining a __hash__ without also defining __eq__ goes against the python data model.

It looks like in the past there was a custom __eq__ but that was removed in #2006 at which time __hash__ should have been removed also.

Its also not necessary in this case as a hash based on the object id is what you get by default.

Its also a performance issue: microbenchmarking reveals that set and dict operations are around 10x slower with custom hash compared to default. I didn't check but I wonder how much this was at issue in #5952 and #5685.

[mtreinish]

Its also a performance issue: microbenchmarking reveals that set and dict operations are around 10x slower with custom hash compared to default. I didn't check but I wonder how much this was at issue in #5952 and #5685.

Well at least for #5952 this won't come up, the retworkx neighbors() function is returning node ids (https://retworkx.readthedocs.io/en/stable/stubs/retworkx.PyDiGraph.html#retworkx.PyDiGraph.neighbors) so it's all ints (also the performance impact of that PR was minimal https://qiskit.github.io/qiskit/#mapping_passes.PassBenchmarks.time_noise_adaptive_layout?commits=5f0fdb6 )

I could definitely see this being a big part of the impact of #5685 though.