There are 4 places that call this helper:
- storage proxy. Callers are rpc verb handlers and already have the proxy
at hands from which they can get the messaging service instance
- repair. There's local-global messaging instance at hands, and the caller
is in verb handler too
- streaming. The caller is verb handler, which is unregistered on stop, so
the messaging service instance can be captured
- migration manager itself. The caller already uses "this", so the messaging
service instance can be get from it
The better approach would be to make get_schema_definition be the method of
migration_manager, but the manager is stopped for real on shutdown, thus
referencing it from the callers might not be safe and needs revisiting. At
the same time the messaging service is always alive, so using its reference
is safe.
Signed-off-by: Pavel Emelyanov <xemul@scylladb.com>