Remove some unnecessary, legacy-looking use of the PROCEDURAL keyword
before LANGUAGE.  We mostly don't use this anymore, so some of these
look a bit old.

There is still some use in pg_dump, which is harder to remove because
it's baked into the archive format, so I'm not touching that.

Discussion: https://www.postgresql.org/message-id/2330919b-62d9-29ac-8de3-58c024fdcb96@2ndquadrant.com