remove unused code around SK_SUPPORT_LEGACY_XFERMODE_PARAM

BUG=skia:

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=4384

Change-Id: I5121acd027d935ade169ff65941f29f654a47bd0
Reviewed-on: https://skia-review.googlesource.com/4384
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>
diff --git a/bench/BlurRoundRectBench.cpp b/bench/BlurRoundRectBench.cpp
index 123e889..6aaa11f 100644
--- a/bench/BlurRoundRectBench.cpp
+++ b/bench/BlurRoundRectBench.cpp
@@ -45,7 +45,7 @@
             SkLayerDrawLooper::LayerInfo info;
             info.fPaintBits = SkLayerDrawLooper::kMaskFilter_Bit
                               | SkLayerDrawLooper::kColorFilter_Bit;
-            info.fColorMode = (SK_XFERMODE_MODE_PARAM)SkBlendMode::kSrc;
+            info.fColorMode = SkBlendMode::kSrc;
             info.fOffset = SkPoint::Make(SkIntToScalar(-1), SkIntToScalar(0));
             info.fPostTranslate = false;
             SkPaint* paint = looperBuilder.addLayerOnTop(info);