The comments were misplaced when adding postgres_fdw.  Fix that by
moving the comments to more appropriate functions.

Author: Etsuro Fujita
Backpatch-through: 9.6
Discussion: https://postgr.es/m/CAPmGK164sAXQtC46mDFyu6d-T25Mzvh5qaRNkit06VMmecYnOA%40mail.gmail.com