pgsql: Remove xmlCleanupParser calls from contrib/xml2.

Log Message:
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Remove xmlCleanupParser calls from contrib/xml2.

These are unnecessary and probably dangerous.  I don't see any immediate
risk situations in the core XML support or contrib/xml2 itself, but there
could be issues with external uses of libxml2, and in any case it's an
accident waiting to happen.

Tags:
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REL8_3_STABLE

Modified Files:
--------------
    pgsql/contrib/xml2:
        xpath.c (r1.16.2.3 -> r1.16.2.4)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/contrib/xml2/xpath.c?r1=1.16.2.3&r2=1.16.2.4)
        xslt_proc.c (r1.9.2.2 -> r1.9.2.3)
        (http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/contrib/xml2/xslt_proc.c?r1=1.9.2.2&r2=1.9.2.3)