Use OutputFilesProvider on filesystem module types

Test: CI
Bug: 339477385
Change-Id: I0902726cfef13c716d73c1abc5c9836bdcf3e10f
diff --git a/filesystem/bootimg.go b/filesystem/bootimg.go
index 352b451..e796ab9 100644
--- a/filesystem/bootimg.go
+++ b/filesystem/bootimg.go
@@ -123,6 +123,8 @@
 
 	b.installDir = android.PathForModuleInstall(ctx, "etc")
 	ctx.InstallFile(b.installDir, b.installFileName(), b.output)
+
+	ctx.SetOutputFiles([]android.Path{b.output}, "")
 }
 
 func (b *bootimg) buildBootImage(ctx android.ModuleContext, vendor bool) android.OutputPath {
@@ -292,13 +294,3 @@
 	}
 	return nil
 }
-
-var _ android.OutputFileProducer = (*bootimg)(nil)
-
-// Implements android.OutputFileProducer
-func (b *bootimg) OutputFiles(tag string) (android.Paths, error) {
-	if tag == "" {
-		return []android.Path{b.output}, nil
-	}
-	return nil, fmt.Errorf("unsupported module reference tag %q", tag)
-}