Remove gratuitous uses of deprecated SELECT INTO

CREATE TABLE AS has been preferred over SELECT INTO (outside of ecpg
and PL/pgSQL) for a long time.  There were still a few uses of SELECT
INTO in tests and documentation, some old, some more recent.  This
changes them to CREATE TABLE AS.  Some occurrences in the tests remain
where they are specifically testing SELECT INTO parsing or similar.

Discussion: https://www.postgresql.org/message-id/flat/96dc0df3-e13a-a85d-d045-d6e2c85218da%40enterprisedb.com

src/test/regress/sql/create_misc.sql

@@ -8,7 +8,7 @@
 
 INSERT INTO tenk2 SELECT * FROM tenk1;
 
-SELECT * INTO TABLE onek2 FROM onek;
+CREATE TABLE onek2 AS SELECT * FROM onek;
 
 INSERT INTO fast_emp4000 SELECT * FROM slow_emp4000;