XFA - Remove namespace from nodes under xfa:data node

- in real life some xfa contains xml like <xfa:data><xfa:Foo><xfa:Bar>...</xfa:data>
    since there are no Foo or Bar in the xfa namespace the JS representation are empty
    and that leads to errors.
  - so the idea is to make all nodes under xfa:data namespace agnostic which means
    that ns are removed from nodes in the parser but only xfa:data descendants.

test/pdfs/xfa_bug1721600.pdf.link

@@ -0,0 +1 @@
+https://bugzilla.mozilla.org/attachment.cgi?id=9232367

test/test_manifest.json

@@ -952,6 +952,15 @@
        "enableXfa": true,
        "type": "eq"
     },
+    {  "id": "xfa_bug1721600",
+       "file": "pdfs/xfa_bug1721600.pdf",
+       "md5": "5f514f476169eeb7254da380a8db495a",
+       "link": true,
+       "rounds": 1,
+       "lastPage": 1,
+       "enableXfa": true,
+       "type": "eq"
+    },
     {  "id": "xfa_bug1720182",
        "file": "pdfs/xfa_bug1720182.pdf",
        "md5": "1351f816f0509fe750ca61ef2bd40872",