bug#67367: gajim-omemo currently not working

[Tomás Ortín]

When running Gajim with the gajim-omemo plugin, the plugin fails with: 
"module 'collections' has no attribute 'MutableMapping'".
The problem seems to be related to protobuf: 
https://dev.gajim.org/gajim/gajim-plugins/-/issues/605

The last version of Gajim, currently not on Guix, is 1.8 and merges 
OMEMO support into Gajim itself, so gajim-omemo will stop being needed. 
However, it indirectly depends on a much more recent version of protobuf 
that is also not on Guix.