Hide SkCanvas::{set,get}DrawFilter

Except for Android, which still makes use of it.

BUG=skia:3587
R=reed@google.com,djsollen@google.com
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1618843002

Review URL: https://codereview.chromium.org/1618843002
diff --git a/src/utils/SkNWayCanvas.cpp b/src/utils/SkNWayCanvas.cpp
index 4f60ca3..23e9b11 100644
--- a/src/utils/SkNWayCanvas.cpp
+++ b/src/utils/SkNWayCanvas.cpp
@@ -292,6 +292,7 @@
     }
 }
 
+#ifdef SK_SUPPORT_LEGACY_DRAWFLTER
 SkDrawFilter* SkNWayCanvas::setDrawFilter(SkDrawFilter* filter) {
     Iter iter(fList);
     while (iter.next()) {
@@ -299,3 +300,4 @@
     }
     return this->INHERITED::setDrawFilter(filter);
 }
+#endif