Remove rule CA2109

[x789]

Removes documentation of rule CA2109.
Rule is removed by PR dotnet/roslyn-analyzers#6198.
Removal of the rule was discussed in dotnet/roslyn-analyzers#5974.

[gewarren]

We'll at least need to add a redirection to https://github.com/dotnet/docs/blob/main/.openpublishing.redirection.fundamentals.json. But I'm wondering if we should also add a new page/section for "deleted" or "obsolete" rules, just so some reference remains. Thoughts?

[Youssef1313]

When CA1801 got deprecated, a note was just added. See #21882

Regardless of the decision, we should be consistent.

[gewarren]

When CA1801 got deprecated, a note was just added. See #21882

Regardless of the decision, we should be consistent.

Yes, I like that better. Leave the article in place but add a prominent banner at the top like #21882.

[x789]

I like the idea that information about the rule is not deleted completely.
From a developer's point of view, the reason why a rule was removed is definitely helpful.

I will adjust the PR so that the information for CA2109 is not removed, but a banner is added (as suggested by @Youssef1313).

Due to my current workload, this may take some days.

[x789]

I started over with a new branch to get a clean commit history. See PR #31797.