The local node's dc:rack pair is cached on system keyspace on start. However, most of other code don't need it as they get dc:rack from topology or directly from snitch. There are few places left that still mess with sysks cache, but they are easy to patch. So after this patch all the core code uses two sources of dc:rack -- topology / snitch -- instead of three.
Closes#15280
* github.com:scylladb/scylladb:
system_keyspace: Don't require snitch argument on start
system_keyspace: Don't cache local dc:rack pair
system_keyspace: Save local info with explicit location
storage_service: Get endpoint location from snitch, not system keyspace
snitch: Introduce and use get_location() method
repair: Local location variables instead of system keyspace's one
repair: Use full endpoint location instead of datacenter part
b062b245ad