Drop obsolete 2fa_home and paraview_home in state dir and add missing server_home (#567)

* Drop obsolete 2fa_home and paraview_home in state dir. The former sounds like
an early version of the current twofactor_home and paraview_home must have been
a part of the now retired image previews so it can safely go.

* Add state server_home which is little used in actual deployments but which
checkconf.py otherwise complains about because it is expected as seen in
https://github.com/ucphhpc/docker-migrid/actions/runs/27134920279/job/80084864641

Author: jonasbardino