[211] Revert uncessary change on State Machine diagram

I thought this fix a problem that display incorrect seprator between compartment but the problem require a fix inside Sirius Web.

Also update the State Machine Diagram test campaign documentation

See https://github.com/eclipse-sirius/sirius-web/issues/3954

Bug: #211 (closed) Signed-off-by: Arthur Daussy arthur.daussy@obeo.fr