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/gm/aaclip.cpp b/gm/aaclip.cpp
index 26a25c1..f00a4cd 100644
--- a/gm/aaclip.cpp
+++ b/gm/aaclip.cpp
@@ -11,7 +11,7 @@
 
 static void do_draw(SkCanvas* canvas, const SkRect& r) {
     SkPaint paint;
-    paint.setXfermodeMode(SkXfermode::kSrc_Mode);
+    paint.setBlendMode(SkBlendMode::kSrc);
     paint.setColor(0x800000FF);
     canvas->drawRect(r, paint);
 }