SkImage now has makeShader to return sk_sp

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1785473002

Review URL: https://codereview.chromium.org/1785473002
diff --git a/src/utils/SkLua.cpp b/src/utils/SkLua.cpp
index b84ba0f..95ca5ad 100644
--- a/src/utils/SkLua.cpp
+++ b/src/utils/SkLua.cpp
@@ -1711,8 +1711,7 @@
 static int limage_newShader(lua_State* L) {
     SkShader::TileMode tmode = SkShader::kClamp_TileMode;
     const SkMatrix* localM = nullptr;
-    SkAutoTUnref<SkShader> shader(get_ref<SkImage>(L, 1)->newShader(tmode, tmode, localM));
-    push_ref(L, shader.get());
+    push_ref(L, get_ref<SkImage>(L, 1)->makeShader(tmode, tmode, localM));
     return 1;
 }