Clean up dead xfermode opts code.

src/opts/SkXfermode_opts_arm_neon.h

-/*
- * Copyright 2015 Google Inc.
- *
- * Use of this source code is governed by a BSD-style license that can be
- * found in the LICENSE file.
- */
-
-#ifndef SkXfermode_opts_arm_neon_DEFINED
-#define SkXfermode_opts_arm_neon_DEFINED
-
-#include "SkXfermode_proccoeff.h"
-
-class SkNEONProcCoeffXfermode : public SkProcCoeffXfermode {
-public:
-    SkNEONProcCoeffXfermode(const ProcCoeff& rec, SkXfermode::Mode mode,
-                            void* procSIMD)
-            : INHERITED(rec, mode), fProcSIMD(procSIMD) {}
-
-    void xfer32(SkPMColor dst[], const SkPMColor src[], int count,
-                const SkAlpha aa[]) const override;
-    void xfer16(uint16_t* SK_RESTRICT dst, const SkPMColor* SK_RESTRICT src,
-                int count, const SkAlpha* SK_RESTRICT aa) const override;
-
-    SK_TO_STRING_OVERRIDE()
-
-private:
-    // void* is used to avoid pulling arm_neon.h in the core and having to build
-    // it with -mfpu=neon.
-    void* fProcSIMD;
-    typedef SkProcCoeffXfermode INHERITED;
-};
-
-extern SkPMColor srcatop_modeproc_neon(SkPMColor src, SkPMColor dst);
-extern SkPMColor dstatop_modeproc_neon(SkPMColor src, SkPMColor dst);
-extern SkPMColor xor_modeproc_neon(SkPMColor src, SkPMColor dst);
-extern SkPMColor plus_modeproc_neon(SkPMColor src, SkPMColor dst);
-extern SkPMColor modulate_modeproc_neon(SkPMColor src, SkPMColor dst);
-
-#endif //#ifdef SkXfermode_opts_arm_neon_DEFINED