remove unused parameter to make android happy (when this header is moved to private)

src/core/SkNx.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 SkNx_DEFINED
 #define SkNx_DEFINED
 
@@ skipping 92 matching lines @@
 };
 
 // The N -> N/2 recursion bottoms out at N == 1, a scalar value.
 template <typename T>
 struct SkNx<1,T> {
     T fVal;
 
     SkNx() = default;
     SkNx(T v) : fVal(v) {}
 
-    T operator[](int k) const {
+    // Android complains against unused parameters, so we guard it
+    T operator[](int SkDEBUGCODE(k)) const {
         SkASSERT(k == 0);
         return fVal;
     }
 
     static SkNx Load(const void* ptr) {
         SkNx v;
         memcpy(&v, ptr, sizeof(T));
         return v;
     }
     void store(void* ptr) const { memcpy(ptr, &fVal, sizeof(T)); }
@@ skipping 177 matching lines @@
     #include "../opts/SkNx_neon.h"
 #endif
 
 SI void Sk4f_ToBytes(uint8_t p[16], const Sk4f& a, const Sk4f& b, const Sk4f& c, const Sk4f& d) {
     SkNx_cast<uint8_t>(SkNx_join(SkNx_join(a,b), SkNx_join(c,d))).store(p);
 }
 
 #undef SI
 
 #endif//SkNx_DEFINED