doc: remove "How is an LTS release cut?" section

The release process is in the Release plan, linked earlier in the doc.
Don't include information here because duplicated information is likely
to drift apart, resulting in contradictions and a lack of clarity about
which document is correct. (I think the text removed is already
out-of-date. I could be wrong, and it doesn't much matter, as it should
be removed anyway.) It's also not entirely clear what the
utility/relevance of this information is in this particular document.

PR-URL: https://github.com/nodejs/node/pull/26955


Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Anatoli Papirovski <apapirovski@mac.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Signed-off-by: Beth Griggs <Bethany.Griggs@uk.ibm.com>