Deleted CF are not cleared if memstore contain entries

While deleting the CF dynamically (without disabling the table), CF dirs are not cleared from FS when region memstore contain entries for that CF. 

Since we delete the CF from FS first and then reopen the region, during reopen RS will flush the memstore content to FS. So deleted CF store will contain the memstore content for the deleted CF. 

So adding back same CF will have old entries.