Remove unused, incorrect XML namespace from bug 346189's reftest

layout/reftests/bugs/346189-1-ref.xul

@@ -4,7 +4,6 @@
 
 <window
   xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"
-  xmlns:html="http://www.w3c.org/1999/xhtml"
   width="400"
   height="600">
 

layout/reftests/bugs/346189-1.xul

@@ -4,7 +4,6 @@
 
 <window
   xmlns="http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"
-  xmlns:html="http://www.w3c.org/1999/xhtml"
   width="400"
   height="600">