Clarify dns.blockESNI wording

[darkexplosiveqwx]

What does this PR aim to accomplish?:

Repaces #2690 and addresses #2690 (comment)

How does this PR accomplish the above?:

As noticed with #2690, I think that dns.blockESNI is obsolete, should I add a deprecation message of some kind?

I do think the current wording can be improved further.

Link documentation PRs if any are needed to support this PR:

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