gh-143928: Docs: remove outdated marshal recursion and object sharing claim

[Sanjay-VK07]

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📚 Documentation preview 📚: https://cpython-previews--144225.org.readthedocs.build/

• Issue: Outdated statement in docs comparing pickle with marshal #143928

[python-cla-bot]

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[StanFromIreland]

Please don't create duplicate PRs, #144025 was opened a few days ago.

[Yashp002]

@Sanjay-VK07 If you're a new contributor you need to sign the contributor license agreement before making any PRs.

Also, you need to claim them first before someone else does and creates a PR. A lot of times core devs need to agree on an issue first to even resolve it, or someone else has already claimed it.

[StanFromIreland]

Also, you need to claim them first before someone else does and creates a PR.

I wouldn't say that's particularly important in the general case, only really newer/more active ones, if I'm working on some 2 year old issue, the chance that some else is in parallel is very very slim, there are 7000 open issues after all.

[Yashp002]

@StanFromIreland yea yea i meant the new ones my bad, @Sanjay-VK07, the ones which have proof of being worked on by someone else recently atleast.