Cleanup some fx_codec_fax.cpp code.

core/src/fxcodec/jbig2/JBig2_Define.h

 // Copyright 2014 PDFium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com
 
 #ifndef _JBIG2_DEFINE_H_
 #define _JBIG2_DEFINE_H_
 
 #include "../../../include/fxcrt/fx_system.h"
 #define JBIG2_memset FXSYS_memset
 #define JBIG2_memcmp FXSYS_memcmp
 #define JBIG2_memcpy FXSYS_memcpy
 #define JBIG2_OOB 1
 
 struct JBig2RegionInfo {
   int32_t width;
   int32_t height;
   int32_t x;
   int32_t y;
   uint8_t flags;
 };
 
 struct JBig2HuffmanCode {
   int32_t codelen;
   int32_t code;
 };
 
-extern "C" {
-void _FaxG4Decode(const uint8_t* src_buf,
-                  FX_DWORD src_size,
-                  int* pbitpos,
-                  uint8_t* dest_buf,
-                  int width,
-                  int height,
-                  int pitch = 0);
-};
-
 #define JBIG2_MAX_REFERRED_SEGMENT_COUNT 64
 #define JBIG2_MAX_EXPORT_SYSMBOLS 65535
 #define JBIG2_MAX_NEW_SYSMBOLS 65535
 #define JBIG2_MAX_PATTERN_INDEX 65535
 #define JBIG2_MAX_IMAGE_SIZE 65535
 
 #endif