pgsql: Remove mention of /contrib README files from documentation

Log Message:
-----------
Remove mention of /contrib README files from documentation because files
are moved to SGML.

Modified Files:
--------------
pgsql/doc/src/sgml:
info.sgml (r1.25 -> r1.26)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/info.sgml?r1=1.25&r2=1.26)