Remove separate files for the initial contents of pg_(sh)description

This data was only in separate files because it was the most convenient
way to handle it with a shell script. Now that we use a general-purpose
programming language, it's easy to assemble the data into the same format
as the rest of the catalogs and output it into postgres.bki. This allows
removal of some special-purpose code from initdb.c.

Discussion: https://www.postgresql.org/message-id/CACPNZCtVFtjHre6hg9dput0qRPp39pzuyA2A6BT8wdgrRy%2BQdA%40mail.gmail.com
Author: John Naylor