Drop creation of `service_levels` and `cdc_generation_descriptions_v2` table creation code since they are no longer needed. Old clusters will still have it because they were created earlier. Also the series contains a small improvement around group0 creation.
No backport needed since this removes functionality.
Closesscylladb/scylladb#29482
* github.com:scylladb/scylladb:
db/system_distributed_keyspace: remove system_distributed_everywhere since it is unused
db/system_distributed_keyspace: drop CDC_TOPOLOGY_DESCRIPTION and CDC_GENERATIONS_V2
db/system_distributed_keyspace: remove unused code
db/system_distributed_keyspace: drop old cdc_generation_descriptions_v2 table
db/system_distributed_keyspace: drop old service_levels table
fix indent after the previous patch
group0: call setup_group0 only when needed
5a887362e3