Remove unused SkDither include

This header is being removed from Skia.

Test: Code still compiles.
Change-Id: I439e46eff48e0853fa5037f7f660e74e7026d87c
diff --git a/core/jni/android/graphics/Bitmap.cpp b/core/jni/android/graphics/Bitmap.cpp
index 0a25271..0c9a85a 100755
--- a/core/jni/android/graphics/Bitmap.cpp
+++ b/core/jni/android/graphics/Bitmap.cpp
@@ -15,7 +15,6 @@
 #include "SkPM4f.h"
 #include "SkPM4fPriv.h"
 #include "GraphicsJNI.h"
-#include "SkDither.h"
 #include "SkUnPreMultiply.h"
 #include "SkStream.h"