If Diskcleanup already removed all replaced updates, it can't to any to further cleanup this folder in Windows Server 2008 R2.
You must live with this folder size or upgrade to Windows Server 2012 R2, here you can use DISM to compact the WinSxS folder more by doing a compression and making the current update permanent by running this DISM command:
dism /online /cleanup-image /startcomponentcleanup /ResetBase