gossip: Sync gossip_digest.idl.hh and application_state.hh
gossip: Sync gossip_digest.idl.hh and application_state.hh

We did the clean up in idl/gossip_digest.idl.hh, but the patch to clean
up gms/application_state.hh was never merged.

To maintain compatibility with previous version of scylla, we can not
change application_state.hh, instead change idl to be sync with
application_state.hh.

Message-Id: <db7b9a783058238603de7407bbb74cd09efe85ee@scylladb.com>

kjniemi/scylla,raphaelsc/scylla,duarten/scylla,scylladb/scylla,kjniemi/scylla,scylladb/scylla,avikivity/scylla,scylladb/scylla,duarten/scylla,kjniemi/scylla,scylladb/scylla,avikivity/scylla,raphaelsc/scylla,avikivity/scylla,duarten/scylla,raphaelsc/scylla