Remove unused matrix param from GrContext/GrDrawTarget rect drawing functions.

R=robertphillips@google.com

Author: bsalomon@google.com

Review URL: https://codereview.chromium.org/441623005
diff --git a/src/gpu/SkGpuDevice.cpp b/src/gpu/SkGpuDevice.cpp
index b1e23f9..7c4f451 100644
--- a/src/gpu/SkGpuDevice.cpp
+++ b/src/gpu/SkGpuDevice.cpp
@@ -1381,7 +1381,7 @@
                                        SkColor2GrColor(paint.getColor());
     SkPaint2GrPaintNoShader(this->context(), paint, paintColor, false, &grPaint);
 
-    fContext->drawRectToRect(grPaint, dstRect, paintRect, NULL);
+    fContext->drawRectToRect(grPaint, dstRect, paintRect);
 }
 
 static bool filter_texture(SkBaseDevice* device, GrContext* context,