This change removes the addition of an empty state to `_endpoint_state_map`.
Instead, a new state is created locally and then published via replicate,
avoiding the issue of an empty state existing in `_endpoint_state_map`
before the preemption point. Since this resolves the issue tested in
`test_gossiper_empty_self_id_on_shadow_round`, the `xfail` mark has been removed.
Fixes: scylladb/scylladb#25831
b34d543f30