content: Cleanup, remove unused SkPorterDuff.h include.

This skia API is marked as deprecated, so we need to remove all usages
of it, to be able to remove it in Skia.

BUG=None
TEST=None
TBR=skyostil@chromium.org

Review URL: https://codereview.chromium.org/669303005

Cr-Commit-Position: refs/heads/master@{#301045}

content/browser/android/system_ui_resource_manager_impl.cc

@@ -16,7 +16,6 @@
 #include "third_party/skia/include/core/SkBitmap.h"
 #include "third_party/skia/include/core/SkCanvas.h"
 #include "third_party/skia/include/core/SkPaint.h"
-#include "third_party/skia/include/effects/SkPorterDuff.h"
 #include "ui/gfx/android/java_bitmap.h"
 #include "ui/gfx/screen.h"