Remove SK_SUPPORT_LEGACY_GRADIENT_DITHERING from Skia proper

src/effects/gradients/SkGradientShader.cpp

Index: src/effects/gradients/SkGradientShader.cpp
diff --git a/src/effects/gradients/SkGradientShader.cpp b/src/effects/gradients/SkGradientShader.cpp
index 88d650c34650d1f8aebddff8d996ff508ad53407..54daa54f566689ea2397ef52bfeddf87040097ab 100644
--- a/src/effects/gradients/SkGradientShader.cpp
+++ b/src/effects/gradients/SkGradientShader.cpp
@@ -290,8 +290,6 @@ bool SkGradientShaderBase::onAsLuminanceColor(SkColor* lum) const {
     return true;
 }
 
-#define SK_SUPPORT_LEGACY_GRADIENT_DITHERING
-
 SkGradientShaderBase::GradientShaderBaseContext::GradientShaderBaseContext(
         const SkGradientShaderBase& shader, const ContextRec& rec)
     : INHERITED(shader, rec)