EXPLAIN shows system fields twice

[agavra]

On master (0de23d2):

ksql> CREATE STREAM foo (ID VARCHAR) WITH (kafka_topic='foo', partitions=1, value_format='json');

 Message
----------------
 Stream created
----------------

ksql> INSERT INTO foo VALUES ('a', '1');
ksql> EXPLAIN SELECT * FROM FOO;

ID                   :
SQL                  : SELECT * FROM FOO;

 Field   | Type
-------------------------------------
 ROWTIME | BIGINT           (system)
 ROWKEY  | VARCHAR(STRING)  (system)
 ROWTIME | BIGINT           (system)
 ROWKEY  | VARCHAR(STRING)  (system)
 ID      | VARCHAR(STRING)
-------------------------------------

Note that ROWTIME/ROWKEY show up twice. Might be related to recent key field work. cc @big-andy-coates

It looks like it's because for SELECT *, ROWTIME and ROWKEY are included in the "value fields".