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/GrDefaultPathRenderer.cpp b/src/gpu/GrDefaultPathRenderer.cpp
index bd9b1ea..dd6ae9d 100644
--- a/src/gpu/GrDefaultPathRenderer.cpp
+++ b/src/gpu/GrDefaultPathRenderer.cpp
@@ -491,7 +491,7 @@
                 bounds = path.getBounds();
             }
             GrDrawTarget::AutoGeometryAndStatePush agasp(target, GrDrawTarget::kPreserve_ASRInit);
-            target->drawSimpleRect(bounds, NULL);
+            target->drawSimpleRect(bounds);
         } else {
             if (passCount > 1) {
                 drawState->enableState(GrDrawState::kNoColorWrites_StateBit);