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

fpdfsdk/fpdfxfa/include/fpdfxfa_app.h

Index: fpdfsdk/fpdfxfa/include/fpdfxfa_app.h
diff --git a/fpdfsdk/fpdfxfa/include/fpdfxfa_app.h b/fpdfsdk/fpdfxfa/include/fpdfxfa_app.h
index 6491781cbe5ce602ae237aa39d623cec5fed1fce..3a61ef40c399e6965a5622a1ec9cec2f3dcc1e75 100644
--- a/fpdfsdk/fpdfxfa/include/fpdfxfa_app.h
+++ b/fpdfsdk/fpdfxfa/include/fpdfxfa_app.h
@@ -51,29 +51,28 @@ class CPDFXFA_App : public IXFA_AppProvider {
   }
 
   void Beep(uint32_t dwType) override;
-  int32_t MsgBox(const CFX_WideStringC& wsMessage,
-                 const CFX_WideStringC& wsTitle,
+  int32_t MsgBox(const CFX_WideString& wsMessage,
+                 const CFX_WideString& wsTitle,
                  uint32_t dwIconType,
                  uint32_t dwButtonType) override;
-  void Response(CFX_WideString& wsAnswer,
-                const CFX_WideStringC& wsQuestion,
-                const CFX_WideStringC& wsTitle,
-                const CFX_WideStringC& wsDefaultAnswer,
-                FX_BOOL bMark) override;
+  CFX_WideString Response(const CFX_WideString& wsQuestion,
+                          const CFX_WideString& wsTitle,
+                          const CFX_WideString& wsDefaultAnswer,
+                          FX_BOOL bMark) override;
 
   int32_t GetDocumentCountInBatch() override;
   int32_t GetCurDocumentInBatch() override;
 
-  IFX_FileRead* DownloadURL(const CFX_WideStringC& wsURL) override;
-  FX_BOOL PostRequestURL(const CFX_WideStringC& wsURL,
-                         const CFX_WideStringC& wsData,
-                         const CFX_WideStringC& wsContentType,
-                         const CFX_WideStringC& wsEncode,
-                         const CFX_WideStringC& wsHeader,
+  IFX_FileRead* DownloadURL(const CFX_WideString& wsURL) override;
+  FX_BOOL PostRequestURL(const CFX_WideString& wsURL,
+                         const CFX_WideString& wsData,
+                         const CFX_WideString& wsContentType,
+                         const CFX_WideString& wsEncode,
+                         const CFX_WideString& wsHeader,
                          CFX_WideString& wsResponse) override;
-  FX_BOOL PutRequestURL(const CFX_WideStringC& wsURL,
-                        const CFX_WideStringC& wsData,
-                        const CFX_WideStringC& wsEncode) override;
+  FX_BOOL PutRequestURL(const CFX_WideString& wsURL,
+                        const CFX_WideString& wsData,
+                        const CFX_WideString& wsEncode) override;
 
   void LoadString(int32_t iStringID, CFX_WideString& wsString) override;
   IFWL_AdapterTimerMgr* GetTimerMgr() override;