Remove dead AbstractFeature.degrade hook

[Hananel-Hazan]

Supersedes #792. Thanks to @Anai-Guo for finding the bug.

What is wrong

AbstractFeature.degrade calls itself, passing an argument the method does not accept:

def degrade(self) -> None:
    return self.degrade(self.value)

degrade takes only self, so this raises TypeError on the very first call, for every feature. It is not even infinite recursion.

Why removing rather than fixing

git log -L 286,295:bindsnet/network/topology_features.py returns a single commit, 4b577e9 "Add topology_features.py". The self-call has been there since the file was created, so the method has never run successfully once.

Nothing calls it. Grepping the whole repo across all file types, the only occurrences of degrade as a method are the definition and the broken self-call inside it. No caller in the library, examples, tests, or docs.

It looks like an intended third per-feature lifecycle hook alongside update and normalize, which MulticompartmentConnection does call generically over its feature pipeline (for f in self.pipeline: f.update(**kwargs) and f.normalize() in topology.py). The matching for f in self.pipeline: f.degrade() loop was never written. Degradation ended up in Degradation.compute instead, which is where the pipeline applies every feature, and which already guards against degrade_function being None.

Fixing the typo would leave two spellings of the same operation, the fixed degrade() being the unguarded one. It would also leave a method on the abstract base that only Degradation can satisfy, since degrade_function is set solely by Degradation.__init__ — calling degrade() on a Weight or Mask would still fail, just with AttributeError.

Risk

None that I can find. Any downstream caller would be crashing today.

Verification

Full suite on this branch: 83 passed. black --check clean.

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