Use merge_csv python_binary.

Instead of using .py file directly.

Bug: 145132366
Test: diff -w out/soong/hiddenapi/hiddenapi-greylist.csv
Change-Id: Ib79019234b4ae05486e831b30d27bd1be3bbba67
diff --git a/java/hiddenapi_singleton.go b/java/hiddenapi_singleton.go
index ad84cde..3243e43 100644
--- a/java/hiddenapi_singleton.go
+++ b/java/hiddenapi_singleton.go
@@ -293,7 +293,7 @@
 	outputPath := hiddenAPISingletonPaths(ctx).metadata
 
 	rule.Command().
-		Tool(android.PathForSource(ctx, "frameworks/base/tools/hiddenapi/merge_csv.py")).
+		BuiltTool(ctx, "merge_csv").
 		Inputs(metadataCSV).
 		Text(">").
 		Output(outputPath)