no need for SK_SUPPORT_LEGACY_CANVAS_IS_REFCNT anymore

BUG=skia:

Change-Id: If0aa01beb8be9bd7d9a3a5b23c795223b02f02d3
Reviewed-on: https://skia-review.googlesource.com/5690
Commit-Queue: Mike Reed <reed@google.com>
Reviewed-by: Mike Reed <reed@google.com>
diff --git a/include/utils/SkNullCanvas.h b/include/utils/SkNullCanvas.h
index 884b68b..8e5e0ac 100644
--- a/include/utils/SkNullCanvas.h
+++ b/include/utils/SkNullCanvas.h
@@ -8,19 +8,11 @@
 #ifndef SkNullCanvas_DEFINED
 #define SkNullCanvas_DEFINED
 
-#include "SkBitmap.h"
-
-class SkCanvas;
+#include "SkCanvas.h"
 
 /**
  * Creates a canvas that draws nothing. This is useful for performance testing.
  */
 SK_API std::unique_ptr<SkCanvas> SkMakeNullCanvas();
 
-#ifdef SK_SUPPORT_LEGACY_CANVAS_IS_REFCNT
-static inline SkCanvas* SkCreateNullCanvas() {
-    return SkMakeNullCanvas().release();
-}
-#endif
-
 #endif