Remove overly-promiscuous SkNx syntax sugar.

tests/SkNxTest.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 "SkNx.h"
 #include "SkRandom.h"
 #include "Test.h"
@@ skipping 28 matching lines @@
     assert_eq(a, 3, 4, 5, 6);
     assert_eq(b, 3, 4, 5, 6);
     assert_eq(c, 3, 4, 5, 6);
     assert_eq(d, 3, 4, 5, 6);
 
     assert_eq(a+b, 6, 8, 10, 12);
     assert_eq(a*b, 9, 16, 25, 36);
     assert_eq(a*b-b, 6, 12, 20, 30);
     assert_eq((a*b).sqrt(), 3, 4, 5, 6);
     assert_eq(a/b, 1, 1, 1, 1);
-    assert_eq(-a, -3, -4, -5, -6);
+    assert_eq(SkNf<N,T>(0)-a, -3, -4, -5, -6);
 
     SkNf<N,T> fours(4);
 
     assert_eq(fours.sqrt(), 2,2,2,2);
     assert_nearly_eq(0.001, fours.rsqrt0(), 0.5, 0.5, 0.5, 0.5);
     assert_nearly_eq(0.001, fours.rsqrt1(), 0.5, 0.5, 0.5, 0.5);
     assert_nearly_eq(0.001, fours.rsqrt2(), 0.5, 0.5, 0.5, 0.5);
 
     assert_eq(              fours.      invert(), 0.25, 0.25, 0.25, 0.25);
     assert_nearly_eq(0.001, fours.approxInvert(), 0.25, 0.25, 0.25, 0.25);
@@ skipping 87 matching lines @@
                  b = rand.nextU() >> 16;
         REPORTER_ASSERT(r, Sk8h::Min(Sk8h(a), Sk8h(b)).kth<0>() == SkTMin(a, b));
     }
 #else
     for (int a = 0; a < (1<<16); a++) {
     for (int b = 0; b < (1<<16); b++) {
         REPORTER_ASSERT(r, Sk8h::Min(Sk8h(a), Sk8h(b)).kth<0>() == SkTMin(a, b));
     }}
 #endif
 }