dao contract: remove serial from proposals in sql

src/contract/dao/wallet.sql

@@ -136,7 +136,6 @@ CREATE TABLE IF NOT EXISTS dao_proposals (
     recv_public BLOB NOT NULL,
     -- Amount of funds that would be sent
     amount BLOB NOT NULL,
-    serial BLOB NOT NULL,
     -- Token ID we propose to send
     sendcoin_token_id BLOB NOT NULL,
     bulla_blind BLOB NOT NULL,