Remove dead code that was reactivated when fixing overrides.

fpdfsdk/src/formfiller/FFL_FormFiller.cpp

Index: fpdfsdk/src/formfiller/FFL_FormFiller.cpp
diff --git a/fpdfsdk/src/formfiller/FFL_FormFiller.cpp b/fpdfsdk/src/formfiller/FFL_FormFiller.cpp
index 1bd29446364b3a0bd774813e01718b0cf34528a5..40d5ede33524f101d307b0c3bd51a1674fb47f2f 100644
--- a/fpdfsdk/src/formfiller/FFL_FormFiller.cpp
+++ b/fpdfsdk/src/formfiller/FFL_FormFiller.cpp
@@ -598,8 +598,6 @@ IFX_SystemHandler* CFFL_FormFiller::GetSystemHandler() const {
   return m_pApp->GetSysHandler();
 }
 
-void CFFL_FormFiller::OnKeyStroke(FX_BOOL bKeyDown, FX_DWORD nFlag) {}
-
 void CFFL_FormFiller::EscapeFiller(CPDFSDK_PageView* pPageView,
                                    FX_BOOL bDestroyPDFWindow) {
   m_bValid = FALSE;