Revert the biggest part of https://github.com/chatmail/core/pull/6722/
in order to fix#6816. Reopens
https://github.com/chatmail/core/issues/6706.
Rationale for reverting instead of fixing is that it's not trivial to
implement "if the chat is encrypted, can_send() returns true": When
sending a message, in order to check whether to encrypt, we load all
peerstates and check whether all of them can be encrypted to
(`should_encrypt()`). We could do this in `can_send()`, but this would
make it quite slow for groups. With multi-transport, the ways of
checking whether to encrypt will be different, so in order not to do
unnecessary work now, this PR just revert parts of
[https://github.com/chatmail/core/pull/6722/](https://github.com/chatmail/core/pull/6817#),
so that we can make things work nicely when multi-transport is merged.
As a quick mitigation, we could increase the timeout from 15s to
something like 1 minute or 1 day: Long enough that usually securejoin
will finish before, but short enough that it's possible to send to old
chats that had a failed securejoin long in the past.
ef798cd86d