bpo-46764: Fix wrapping bound method with @classmethod

[msullivan]

Since #8405, @classmethod now has special case behavior to call its
argument's tp_descr_get if it exists. This breaks wrapping a bound
method with it, since bound method's have a do-nothing tp_descr_get.

Drop that do-nothing tp_descr_get.

https://bugs.python.org/issue46764

[msullivan]

Looking at the history, it looks like method_descr_get used to handle unbound methods. This became dead in python 3, and that logic was cleaned up in #12169, but I think it should basically be sound to just drop it.

(Of course, things that directly check for the presence of __get__, like classmethod, will be affected)

[JelleZijlstra]

@rhettinger do you still want to look at this? Would be good to get it in before the feature freeze (this Friday).

[bedevere-bot]

🤖 New build scheduled with the buildbot fleet by @JelleZijlstra for commit fcbe203 🤖

If you want to schedule another build, you need to add the ":hammer: test-with-buildbots" label again.

[rhettinger]

@JelleZijlstra I'm holding off on this one for a bit. As a bug fix, it can be committed after the feature freeze. The contending issue is that I'm working on deprecating the behavior — it is hard to use, it broke too many things, the fixed are making it worse, and since 3.10 we have a viable clean alternate path using __wrapped.

[JelleZijlstra]

Right, the descriptor behavior of classmethod has been problematic (#89519 (comment) for reference). I'll leave this to you.