remove unused mode parameter from SkMergeImageFilter

Bug: skia:
Change-Id: Iaa46aaef130a337987c3528685f59c56387d4a7d
Reviewed-on: https://skia-review.googlesource.com/20210
Reviewed-by: Florin Malita <fmalita@chromium.org>
Commit-Queue: Mike Reed <reed@google.com>
diff --git a/bench/MergeBench.cpp b/bench/MergeBench.cpp
index c37d198..10aa8b8 100644
--- a/bench/MergeBench.cpp
+++ b/bench/MergeBench.cpp
@@ -81,7 +81,7 @@
 private:
     sk_sp<SkImageFilter> mergeBitmaps() {
         return SkMergeImageFilter::Make(SkImageSource::Make(fCheckerboard),
-                                        SkImageSource::Make(fImage), SkBlendMode::kSrcOver);
+                                        SkImageSource::Make(fImage));
     }
 
     bool fIsSmall;