Node-isSameNode.html: Fix duplicate test name error

[cvrebert]

Rename "elements should be compared on reference" tests to avoid error from test harness:

Duplicate test name: elements should be compared on reference

[wpt-pr-bot]

Notifying @Ms2ger, @ayg, @jdm, @zcorpan, and @zqzhang. (Learn how reviewing works.)

[wpt-stability-bot]

Firefox (nightly channel)

Testing web-platform-tests at revision b011ca8
Using browser at version BuildID 20170123125947; SourceStamp 36486fdc3813ef7943ae5b07b4128866d1938a6c
Starting 10 test iterations
All results were stable

All results

/dom/nodes/Node-isSameNode.html

Subtest	Results
	OK
elements should be compared on reference (namespaced element)	PASS
elements should be compared on reference (namespaced attribute)	PASS
document fragments should be compared on reference	PASS
doctypes should be comapred on reference	PASS
documents should not be compared on reference	PASS
comments should be compared on reference	PASS
text nodes should be compared on reference	PASS
processing instructions should be compared on reference	PASS

[wpt-stability-bot]

Chrome (unstable channel)

Testing web-platform-tests at revision b011ca8
Using browser at version 55.0.2883.75
Starting 10 test iterations
All results were stable

All results

/dom/nodes/Node-isSameNode.html

Subtest	Results
	OK
elements should be compared on reference (namespaced element)	PASS
elements should be compared on reference (namespaced attribute)	PASS
document fragments should be compared on reference	PASS
doctypes should be comapred on reference	PASS
documents should not be compared on reference	PASS
comments should be compared on reference	PASS
text nodes should be compared on reference	PASS
processing instructions should be compared on reference	PASS