pgsql: Remove some cross-references that don't seem to work in HISTORY

Log Message:
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Remove some cross-references that don't seem to work in HISTORY
generation ... we should figure this out later ...

Modified Files:
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pgsql/doc/src/sgml:
release.sgml (r1.514 -> r1.515)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/release.sgml?r1=1.514&r2=1.515)