mautrix-go now include a cryptohelper package, which solves all my
issues and just works. the setting is now on by default, however
packages are not yet built with it.
also some more attempts at fixing it, so far all i've found is that if
we don't delete the cryptoStore, the matrix client also gets the same
error we do if it send s a message to us (no session with given ID
found).
since this is so broken and requires CGO deps, E2EE support is now only
included with "make E2EE=on ...". The option to enable will then appear
in settings.
