Clean up dead xfermode opts code.

src/opts/SkXfermode_opts_none.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkXfermode.h"
 #include "SkXfermode_proccoeff.h"
 
-// The prototypes below are for Clang
-extern SkProcCoeffXfermode* SkPlatformXfermodeFactory(const ProcCoeff& rec,
-                                                      SkXfermode::Mode mode);
 
-extern SkXfermodeProc SkPlatformXfermodeProcFactory(SkXfermode::Mode mode);
-
-SkProcCoeffXfermode* SkPlatformXfermodeFactory(const ProcCoeff& rec,
-                                               SkXfermode::Mode mode) {
+SkProcCoeffXfermode* SkPlatformXfermodeFactory(const ProcCoeff& rec, SkXfermode::Mode mode);
+SkProcCoeffXfermode* SkPlatformXfermodeFactory(const ProcCoeff& rec, SkXfermode::Mode mode) {
     return NULL;
 }
 
+SkXfermodeProc SkPlatformXfermodeProcFactory(SkXfermode::Mode mode);
 SkXfermodeProc SkPlatformXfermodeProcFactory(SkXfermode::Mode mode) {
     return NULL;
 }