The statement issuers of this node's pools, one for each pool.

A pool starts its own macula_statement_issuer here, for the node identity key it holds, with itself as the owner. A child is temporary: it ends with its owner and this supervisor never restarts it, so a pool that loses its issuer starts a new one itself. The identity key reaches the issuer as a function that returns it, so no start argument this supervisor keeps, and no report of a refused start, holds the key.