Remove SK_SUPPORT_LEGACY_ADDOVAL

BUG=458898
TBR=reed@google.com
NOTRY=true

Review URL: https://codereview.chromium.org/926403002

Cr-Commit-Position: refs/heads/master@{#319598}

cc/trees/layer_tree_host_pixeltest_masks.cc

@@ -395,8 +395,8 @@ TEST_P(LayerTreeHostMasksForBackgroundFiltersPixelTest,
 
   float percentage_pixels_large_error = 2.5f;  // 2.5%, ~1600px / (256*256)
   float percentage_pixels_small_error = 0.0f;
-  float average_error_allowed_in_bad_pixels = 60.0f;
-  int large_error_allowed = 100;
+  float average_error_allowed_in_bad_pixels = 100.0f;
+  int large_error_allowed = 256;
   int small_error_allowed = 0;
   pixel_comparator_.reset(new FuzzyPixelComparator(
       true,  // discard_alpha

skia/config/SkUserConfig.h

@@ -261,10 +261,6 @@ SK_API void SkDebugf_FileLine(const char* file, int line, bool fatal,
 #   define SK_IGNORE_GPU_DITHER
 #endif
 
-#ifndef SK_SUPPORT_LEGACY_ADDOVAL
-#   define SK_SUPPORT_LEGACY_ADDOVAL
-#endif
-
 #ifndef    SK_LEGACY_STROKE_CURVES
 #   define SK_LEGACY_STROKE_CURVES
 #endif