remove separate postgres.(sh)description files

I'm guessing the initial data for pg_(sh)description is output into
separate files because it was too difficult for the traditional shell
script to maintain enough state to do otherwise. With Perl, it's just
as easy to assemble the data into the same format as the rest of the
catalogs and then let the generic code path output it into
postgres.bki. The attached patch does that and simplifies the catalog
makefile and initdb.c. I'll add a commitfest entry for this.
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John Naylor                https://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services