The documentation as well as source code comments weren't entirely
clear whether SELECT INTO was truly deprecated (thus in theory
destined to be removed eventually), or just a less recommended
variant.  After discussion, it appears that other implementations also
use SELECT INTO in direct SQL in a way similar to PostgreSQL, so it
seems worth keeping it for compatibility.  Update the language in the
documentation to that effect.

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