service/migration_manager: Implement announce_column_family_drop()
service/migration_manager: Implement announce_column_family_drop()

Signed-off-by: Pekka Enberg <add4fcd06328a394f0ad91feda7ee057316dc5ed@cloudius-systems.com>

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