Cleanup state/inventory/config inter-references

[Fizzadar]

See: https://github.com/Fizzadar/pyinfra/pull/881/commits/947f8f691aec10e8ed963991db49afa36a58abc5

First thought move state.active_hosts (and other *_hosts variables) to inventory, since that's where they are accessed from anyway, this means Inventory.state reference can be dropped entirely.