Remove uncessary include for SkPorterDuff.h

Change-Id: Ibcbed5dd2dc327821fc26e87191185f0069c9911
diff --git a/libs/hwui/SkiaCanvas.cpp b/libs/hwui/SkiaCanvas.cpp
index efbb709..71088b7 100644
--- a/libs/hwui/SkiaCanvas.cpp
+++ b/libs/hwui/SkiaCanvas.cpp
@@ -22,7 +22,6 @@
 #include <SkDeque.h>
 #include <SkDrawFilter.h>
 #include <SkGraphics.h>
-#include <SkPorterDuff.h>
 #include <SkShader.h>
 #include <SkTArray.h>
 #include <SkTemplates.h>