Remove EXPLAIN from comment [#143465051]

atmsort.pl kinda indiscriminately treat lines (even comments) containing
the character sequence EXPLAIN...SELECT as a hint of the following lines
being a plan. Which is wrong, when the word selector also matches that.

Changing the comments for now, before we really fix atmsort. This will
give us much better failures.

src/test/regress/expected/bfv_partition.out

@@ -1817,9 +1817,9 @@ SELECT * FROM foo FULL JOIN bar ON foo.a = bar.b;
    | 2 | 3
 (2 rows)
 
----
---- Test EXPLAIN on a hash agg that has a Sequence + Partition Selector below it.
----
+--
+-- Test a hash agg that has a Sequence + Partition Selector below it.
+--
 -- SETUP
 -- start_ignore
 DROP TABLE IF EXISTS bar;

src/test/regress/expected/bfv_partition_optimizer.out

@@ -1818,9 +1818,9 @@ SELECT * FROM foo FULL JOIN bar ON foo.a = bar.b;
    | 2 | 3
 (2 rows)
 
----
---- Test EXPLAIN on a hash agg that has a Sequence + Partition Selector below it.
----
+--
+-- Test a hash agg that has a Sequence + Partition Selector below it.
+--
 -- SETUP
 -- start_ignore
 DROP TABLE IF EXISTS bar;

src/test/regress/sql/bfv_partition.sql

@@ -746,9 +746,9 @@ INSERT INTO bar VALUES (2,3);
 SELECT * FROM foo FULL JOIN bar ON foo.a = bar.b;
 
 
----
---- Test EXPLAIN on a hash agg that has a Sequence + Partition Selector below it.
----
+--
+-- Test a hash agg that has a Sequence + Partition Selector below it.
+--
 
 -- SETUP
 -- start_ignore