Bump ome.omero_prometheus_exporter to 0.3.3

[sbesson]

Include omero_prometheus_tools bug fix as well as the cleanup of former Python 2-based deployment.

• [x] ome-training-4.openmicroscopy.org
• [x] ome-dundeeomero.openmicroscopy.org
• [x] ome-demoserver.openmicroscopy.org
• [x] outreach.openmicroscopy.org
• [x] workshop.openmicroscopy.org
• [x] ome-training-3.openmicroscopy.org
• [x] pub-omero.openmicroscopy.org