Revert[8] "replace SkXfermode obj with SkBlendMode enum in paints"

This reverts commit c245574ba3d0e2ade6c94b2812de3baa383bf4c4.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2396953002

TBR=

Review-Url: https://codereview.chromium.org/2396953002
diff --git a/tests/ReadPixelsTest.cpp b/tests/ReadPixelsTest.cpp
index 5fbaf9b..008781c 100644
--- a/tests/ReadPixelsTest.cpp
+++ b/tests/ReadPixelsTest.cpp
@@ -113,7 +113,7 @@
     canvas->setMatrix(SkMatrix::I());
     canvas->clipRect(DEV_RECT_S, SkCanvas::kReplace_Op);
     SkPaint paint;
-    paint.setXfermodeMode(SkXfermode::kSrc_Mode);
+    paint.setBlendMode(SkBlendMode::kSrc);
     canvas->drawBitmap(make_src_bitmap(), 0, 0, &paint);
     canvas->restore();
 }