Remove two unnecessary operations.

Remove two unnecessary operations.

<pre>
[[local]:5432] matt@~ =# EXPLAIN ANALYZE SELECT 'x' <> 'x' FROM generate_series(1,100000);
                                                       QUERY PLAN
-------------------------------------------------------------------------------------------------------------------------
 Function Scan on generate_series  (cost=0.00..10.00 rows=1000 width=0) (actual time=22.346..45.794 rows=100000 loops=1)
 Planning time: 0.042 ms
 Execution time: 59.130 ms
(3 rows)

Time: 59.744 ms
[[local]:5432] matt@~ =# EXPLAIN ANALYZE SELECT 'x' <> 'y' FROM generate_series(1,100000);
                                                       QUERY PLAN
-------------------------------------------------------------------------------------------------------------------------
 Function Scan on generate_series  (cost=0.00..10.00 rows=1000 width=0) (actual time=21.784..45.676 rows=100000 loops=1)
 Planning time: 0.043 ms
 Execution time: 59.294 ms
(3 rows)

Time: 59.663 ms
</pre>