Consider removing "Experimental" for the open systems simulator

[kuzminrobin]

Sparse Simulator Sec: Cassandra: Apologies that this is somewhat tangential, but I note from this description [Sparse Simulator Sec] that the new simulator [Sparse Simulator] is not considered experimental like the open systems simulator.

Given that the open systems simulator represents a very basic workflow, we may want to consider removing the experimental label ASAP to avoid inadvertently communicating to users that the more specialized workflow for this simulator [Sparse Simulator] isn't prioritized over the open systems simulator.

The corresponding documentation pages (that will also need an update if any) are mentioned here.