pgsql: Update release checklist to reflect that HISTORY and INSTALL

Log Message:
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Update release checklist to reflect that HISTORY and INSTALL don't
need to be created by hand anymore.

Tags:
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REL8_0_STABLE

Modified Files:
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pgsql/src/tools:
RELEASE_CHANGES (r1.52.4.1 -> r1.52.4.2)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/tools/RELEASE_CHANGES.diff?r1=1.52.4.1&r2=1.52.4.2)