Remove SK_SUPPORT_LEGACY_DITHERING

Change-Id: I0e896e19a180c6d3eb8b3e16f05f962951fc1a17
Reviewed-on: https://chromium-review.googlesource.com/545815Reviewed-by: Mike Klein <mtklein@chromium.org>
Commit-Queue: Florin Malita <fmalita@chromium.org>
Cr-Commit-Position: refs/heads/master@{#481952}

skia/config/SkUserConfig.h

@@ -208,10 +208,6 @@ SK_API void SkDebugf_FileLine(const char* file, int line, bool fatal,
 #define SK_DISABLE_DEFERRED_PROXIES
 #endif
 
-#ifndef SK_SUPPORT_LEGACY_DITHERING
-#define SK_SUPPORT_LEGACY_DITHERING
-#endif
-
 #ifndef SK_SUPPORT_LEGACY_TILED_BITMAPS
 #define SK_SUPPORT_LEGACY_TILED_BITMAPS
 #endif