Remove spurious XFA unsupported warning on XFA branch
Remove spurious XFA unsupported warning on XFA branch

R=bo_xu@foxitsoftware.com

Review URL: https://codereview.chromium.org/818543002

DrAlexx/pdfium,andoma/pdfium,DrAlexx/pdfium,DrAlexx/pdfium,DrAlexx/pdfium,andoma/pdfium,andoma/pdfium,andoma/pdfium