After importing a Cloud Controller (CC) database it's possible to check "Use the default Cloud Controller database" but only after creating a key in the ledger.
To check "Use the default Cloud Controller database":
There is no way to go back to "Use the default Cloud Controller database" and zero keys in "Encryption key ledger". The ledger is the preferred way to set encryption keys, though, since "Cloud Controller database encryption key" is a legacy field from before the tile supported rotating encryption keys.