Remove some c_str() calls from StringCs in xfa docs.

xfa/fxfa/app/xfa_fffield.cpp

Index: xfa/fxfa/app/xfa_fffield.cpp
diff --git a/xfa/fxfa/app/xfa_fffield.cpp b/xfa/fxfa/app/xfa_fffield.cpp
index cb65a0b9a93862ddc913c4cc045b03a979b40c53..7cf0c6e3fcbbef563dfd4b768cf8baf4d2a84bce 100644
--- a/xfa/fxfa/app/xfa_fffield.cpp
+++ b/xfa/fxfa/app/xfa_fffield.cpp
@@ -725,8 +725,8 @@ int32_t CXFA_FFField::CalculateWidgetAcc(CXFA_WidgetAcc* pAcc) {
           wsMessage += wsWarning;
           CFX_WideString wsTitle;
           pAppProvider->LoadString(XFA_IDS_CalcOverride, wsTitle);
-          pAppProvider->MsgBox(wsMessage.AsStringC(), wsTitle.AsStringC(),
-                               XFA_MBICON_Warning, XFA_MB_OK);
+          pAppProvider->MsgBox(wsMessage, wsTitle, XFA_MBICON_Warning,
+                               XFA_MB_OK);
         }
       }
         return 0;
@@ -757,8 +757,7 @@ int32_t CXFA_FFField::CalculateWidgetAcc(CXFA_WidgetAcc* pAcc) {
           wsMessage += wsWarning;
           CFX_WideString wsTitle;
           pAppProvider->LoadString(XFA_IDS_CalcOverride, wsTitle);
-          if (pAppProvider->MsgBox(wsMessage.AsStringC(), wsTitle.AsStringC(),
-                                   XFA_MBICON_Warning,
+          if (pAppProvider->MsgBox(wsMessage, wsTitle, XFA_MBICON_Warning,
                                    XFA_MB_YesNo) == XFA_IDYes) {
             pAcc->GetNode()->SetFlag(XFA_NODEFLAG_UserInteractive, false);
             return 1;