Set information_schema.tables.commit_action to null

The commit action of temporary tables is currently not cataloged, so
we can't easily show it.  The previous value was outdated from before
we had different commit actions.

doc/src/sgml/information_schema.sgml

@@ -5416,12 +5416,7 @@ ORDER BY c.ordinal_position;
      <row>
       <entry><literal>commit_action</literal></entry>
       <entry><type>character_data</type></entry>
-      <entry>
-       If the table is a temporary table, then
-       <literal>PRESERVE</literal>, else null.  (The SQL standard
-       defines other commit actions for temporary tables, which are
-       not supported by <productname>PostgreSQL</>.)
-      </entry>
+      <entry>Not yet implemented</entry>
      </row>
     </tbody>
    </tgroup>

src/backend/catalog/information_schema.sql

@@ -1862,10 +1862,7 @@ CREATE VIEW tables AS
                 THEN 'YES' ELSE 'NO' END AS yes_or_no) AS is_insertable_into,
 
            CAST(CASE WHEN t.typname IS NOT NULL THEN 'YES' ELSE 'NO' END AS yes_or_no) AS is_typed,
-           CAST(
-             CASE WHEN nc.oid = pg_my_temp_schema() THEN 'PRESERVE' -- FIXME
-                  ELSE null END
-             AS character_data) AS commit_action
+           CAST(null AS character_data) AS commit_action
 
     FROM pg_namespace nc JOIN pg_class c ON (nc.oid = c.relnamespace)
            LEFT JOIN (pg_type t JOIN pg_namespace nt ON (t.typnamespace = nt.oid)) ON (c.reloftype = t.oid)