Revert of SkNx miplevel building

src/opts/SkNx_sse.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_sse_DEFINED
 #define SkNx_sse_DEFINED
 
@@ skipping 361 matching lines @@
 
 static inline void Sk4f_ToBytes(uint8_t bytes[16],
                                 const Sk4f& a, const Sk4f& b, const Sk4f& c, const Sk4f& d) {
     _mm_storeu_si128((__m128i*)bytes,
                      _mm_packus_epi16(_mm_packus_epi16(_mm_cvttps_epi32(a.fVec),
                                                        _mm_cvttps_epi32(b.fVec)),
                                       _mm_packus_epi16(_mm_cvttps_epi32(c.fVec),
                                                        _mm_cvttps_epi32(d.fVec))));
 }
 
-template<> inline Sk4h SkNx_cast<uint16_t, uint8_t, 4>(const Sk4b& src) {
-    return _mm_unpacklo_epi8(src.fVec, _mm_setzero_si128());
-}
-
-template<> inline Sk4b SkNx_cast<uint8_t, uint16_t, 4>(const Sk4h& src) {
-    return _mm_packus_epi16(src.fVec, src.fVec);
-}
-
 
 }  // namespace
 
 #endif//SkNx_sse_DEFINED