Remove CXFA_FFDoc::m_pXMLDoc.

The member is completely unused.

Change-Id: Ibcd67f41e72746aa42b63a212254ebeb6c613001
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/84770
Reviewed-by: Hui Yingst <nigi@chromium.org>
Commit-Queue: Tom Sepez <tsepez@chromium.org>

xfa/fxfa/cxfa_ffdoc.h

diff --git a/xfa/fxfa/cxfa_ffdoc.h b/xfa/fxfa/cxfa_ffdoc.h
index c0880fb..d108cc3 100644
--- a/xfa/fxfa/cxfa_ffdoc.h
+++ b/xfa/fxfa/cxfa_ffdoc.h
@@ -184,7 +184,6 @@
   UnownedPtr<CallbackIface> const m_pDocEnvironment;
   UnownedPtr<CPDF_Document> const m_pPDFDoc;
   UnownedPtr<cppgc::Heap> const m_pHeap;
-  UnownedPtr<CFX_XMLDocument> m_pXMLDoc;
   cppgc::Member<CXFA_FFApp> const m_pApp;
   cppgc::Member<CXFA_FFNotify> m_pNotify;
   cppgc::Member<CXFA_Document> m_pDocument;