remove switchToBasic fixme

io/directory.go

@@ -416,14 +416,6 @@ func (d *HAMTDirectory) switchToBasic(ctx context.Context) (*BasicDirectory, err
 
 		return nil
 	})
-	// FIXME: The above was adapted from SwitchToSharding. We can probably optimize:
-	//  2. Do not enumerate all link from scratch (harder than previous
-	//     item). We call this function only from the UpgradeableDirectory
-	//     when we went below the threshold: the detection will be done through
-	//     (partial) enumeration. We may be able to reuse some of that work
-	//     (likely retaining the links in a cache). (All this is uncertain
-	//     at this point as we don't know how partial enumeration will be
-	//     implemented.)
 
 	return basicDir, nil
 }