Remove mysterious clearCachedNode call in JRuby that breaks Blather

It was previously described at "weird" and even the original author
cannot remember why it is there. Its presence causes Blather's
Blather::XMPPNode subclass instances to be recreated where they become
generic Nokogiri::XML::Element instances instead.

Closes sparklemotion#1708.

ext/java/nokogiri/XmlNode.java

@@ -464,9 +464,6 @@ public void relink_namespace(ThreadContext context) {
             return;
         }
 
-        // TODO: this feels kind of weird, why are we clearing the XmlNode
-        // cache here !!!
-        clearCachedNode(node);
         Element e = (Element) node;
 
         // disable error checking to prevent lines like the following