[emacs] thread view is showing all messages

[Rafael Avila de Espindola]

The documentation says that:

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By default, various components of email messages, (citations,
signatures, already-read messages),  are hidden.
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Unfortunately that is not what I am experiencing with notmuch 0.23.1.
Any time I open a thread I see all the messages in it. I can hide each
one with <RET>, but that is fairly inconvenient.

Cheers,
Rafael