Just an update, as I managed to 'clean' juju status from 'obsolete' machines.
Once I deleted non-voting machines with 'nova delete', and waited for some time, I run 'juju ensure-availability' again. Juju then 'removed' the machines from 'state-server-member-state' (group? option?). After that I used 'juju remove-machine --force' to get rid of those machines.
Just an update, as I managed to 'clean' juju status from 'obsolete' machines.
Once I deleted non-voting machines with 'nova delete', and waited for some time, I run 'juju ensure- availability' again. Juju then 'removed' the machines from 'state- server- member- state' (group? option?). After that I used 'juju remove-machine --force' to get rid of those machines.