Remove GraphicsContext::strokeArc, which is unused.

Source/core/platform/graphics/GraphicsContext.h

Index: Source/core/platform/graphics/GraphicsContext.h
diff --git a/Source/core/platform/graphics/GraphicsContext.h b/Source/core/platform/graphics/GraphicsContext.h
index 9d9a18855ab3258e39cb6093ffafac79cfe6a7f6..d802307c273f5f792011027bcd1c7f81d68da67b 100644
--- a/Source/core/platform/graphics/GraphicsContext.h
+++ b/Source/core/platform/graphics/GraphicsContext.h
@@ -225,9 +225,6 @@ namespace WebCore {
         void fillEllipse(const FloatRect&);
         void strokeEllipse(const FloatRect&);
 
-        // Arc drawing (used by border-radius in CSS) just supports stroking at the moment.
-        void strokeArc(const IntRect&, int startAngle, int angleSpan);
-
         void fillRect(const FloatRect&);
         void fillRect(const FloatRect&, const Color&, ColorSpace);
         void fillRect(const FloatRect&, Generator&);