Very minor: Remove outdated comment from rabbit_msg_store (backport #14190)

[mergify]

Proposed Changes

Sorry for providing a PR instead of asking the question: Is that correct that "The value close is never stored in the file handle ets since commit 32816c0."?

I found this comment while investigating #14181. As far as I can see the value can never be close so it cannot be the cause of the bug.

During the same investigation I got another question. Comment says (https://github.com/rabbitmq/rabbitmq-server/blob/v4.1.2/deps/rabbit/src/rabbit_msg_store.erl#L520-L522)

Get index for all Msgids in File.
It's possible that we get no results here if compaction
was in progress. That's OK: we will try again with those
MsgIds to get them from the new file.

But compaction (as opposed to combination) doesn't create new files. Only moves messages within the same file. How can a message be moved to a "new file" (assuming it has positive refcount)?

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Further Comments

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This is an automatic backport of pull request #14190 done by [Mergify](https://mergify.com).