Revert of Make the CPDFXFA_App non-global

fpdfsdk/fpdfformfill.cpp

Index: fpdfsdk/fpdfformfill.cpp
diff --git a/fpdfsdk/fpdfformfill.cpp b/fpdfsdk/fpdfformfill.cpp
index 0f44b1dfa2be6bfeff9dce3942ee41cf671356a5..34e206d6bc67eaa6a0cebfc0b3cecf3cff99f737 100644
--- a/fpdfsdk/fpdfformfill.cpp
+++ b/fpdfsdk/fpdfformfill.cpp
@@ -258,6 +258,7 @@
 
 #ifdef PDF_ENABLE_XFA
   pDocument->SetFormFillEnv(pFormFillEnv);
+  CPDFXFA_App::GetInstance()->AddFormFillEnv(pFormFillEnv);
 #endif  // PDF_ENABLE_XFA
 
   return pFormFillEnv;
@@ -272,6 +273,8 @@
       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();