use Make instead of Create to return a shared shader

Partially updated call sites. Undefine the flag in SkSHader.h to convert the remaining sites.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1772463002

Review URL: https://codereview.chromium.org/1772463002
diff --git a/samplecode/Sample2PtRadial.cpp b/samplecode/Sample2PtRadial.cpp
index 07efd0a..c32025e 100644
--- a/samplecode/Sample2PtRadial.cpp
+++ b/samplecode/Sample2PtRadial.cpp
@@ -33,12 +33,10 @@
         SkScalar r0 = 100;
         SkPoint c1 = { 100, 100 };
         SkScalar r1 = 100;
-        SkShader* s = SkGradientShader::CreateTwoPointConical(c0, r0, c1, r1, colors,
-                                                             nullptr, 2,
-                                                             SkShader::kClamp_TileMode);
-
         SkPaint paint;
-        paint.setShader(s)->unref();
+        paint.setShader(SkGradientShader::MakeTwoPointConical(c0, r0, c1, r1, colors,
+                                                             nullptr, 2,
+                                                             SkShader::kClamp_TileMode));
         canvas->drawPaint(paint);
     }