Fix: cib: Prevent use-after-free when invoking "cibadmin --delete-all --xpath"

An xpath like "//*[contains(@id,'rsc1')]" or a bad xpath can match xml
nodes that have parent-child relationships among them. That would cause
use-after-free when invoking "cibadmin --delete-all --xpath" with it.

This commit deduplicates xml nodes from xpathObj->nodesetval->nodeTab
as long as any of their parents are also in there.