gh-152397: Remove external PEP reference

[rhettinger]

Apply Ned's suggested edits.

• Issue: the itertools.chain.from_iterable docs should gain a short note pointing readers PEP 798 alternative #152397

[rhettinger]

@nedbat: My preference would to omit, "In Python 3.15 and later," and leave the versioning information in the referenced section rather than repeat it.

[read-the-docs-community]

Documentation build overview

📚 cpython-previews | 🛠️ Build #33345076 | 📁 Comparing d6baa89 against main (306d7a7)

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4 files changed

± howto/curses.html
± library/itertools.html
± reference/expressions.html
± whatsnew/changelog.html

[nedbat]

@nedbat: My preference would to omit, "In Python 3.15 and later," and leave the versioning information in the referenced section rather than repeat it.

Yes, that is what I did in my pull request: #152462

[nedbat]

This only updates one of the references. Is there a reason we're not using #152462?