Reland: Make the CPDFXFA_App non-global

fpdfsdk/fpdfformfill.cpp

Index: fpdfsdk/fpdfformfill.cpp
diff --git a/fpdfsdk/fpdfformfill.cpp b/fpdfsdk/fpdfformfill.cpp
index 34e206d6bc67eaa6a0cebfc0b3cecf3cff99f737..0f44b1dfa2be6bfeff9dce3942ee41cf671356a5 100644
--- a/fpdfsdk/fpdfformfill.cpp
+++ b/fpdfsdk/fpdfformfill.cpp
@@ -258,7 +258,6 @@ FPDFDOC_InitFormFillEnvironment(FPDF_DOCUMENT document,
 
 #ifdef PDF_ENABLE_XFA
   pDocument->SetFormFillEnv(pFormFillEnv);
-  CPDFXFA_App::GetInstance()->AddFormFillEnv(pFormFillEnv);
 #endif  // PDF_ENABLE_XFA
 
   return pFormFillEnv;
@@ -273,8 +272,6 @@ FPDFDOC_ExitFormFillEnvironment(FPDF_FORMHANDLE hHandle) {
       HandleToCPDFSDKEnvironment(hHandle);
 
 #ifdef PDF_ENABLE_XFA
-  CPDFXFA_App::GetInstance()->RemoveFormFillEnv(pFormFillEnv);
-
   // Reset the focused annotations and remove the SDK document from the
   // XFA document.
   pFormFillEnv->ClearAllFocusedAnnots();