JJ: Description from the destination commit:

+ make_denom_group

JJ: Description from source commit:
ok denom group + exchange_sig

src/api.ml

@@ -1229,10 +1229,6 @@ module ExchangeKeysResponse = struct
     hard_limits: AccountLimit.t list;
     zero_limits: ZeroLimitedOperation.t list;
     denominations: DenomGroup.t list;
-    (* Compact EdDSA signature (binary-only) over the
-       contatentation of all of the master_sigs (in reverse
-       chronological order by group) in the arrays under
-       "denominations" *)
     exchange_sig: ExchangeKeySet.t;
     exchange_pub: EddsaPublicKey.t;
     recoup: RecoupDenoms.t list;