txdb: fix iterators.

lib/bcoin/txdb.js

@@ -1333,7 +1333,7 @@ TXDB.prototype.getHistoryHashes = function getHistoryHashes(account, callback) {
         return key[1];
       }
       key = layout.tt(key);
-      return key[0];
+      return key;
     }
   }, callback);
 };
@@ -1363,7 +1363,7 @@ TXDB.prototype.getUnconfirmedHashes = function getUnconfirmedHashes(account, cal
         return key[1];
       }
       key = layout.pp(key);
-      return key[0];
+      return key;
     }
   }, callback);
 };