Unnecessary check

[JensRantil]

https://github.com/fzakaria/space-saving/blob/master/src/main/java/com/github/fzakaria/topk/spacesaving/StreamSummary.java#L101 can be removed. Remove will remove if it's there, otherwise do nothing.

[fzakaria]

that's true.
I think I wrote it following some whitepaper (url at the top) -- so i probably made it explicit.
If you'd like to submit a PR I'd be happy to accept.