Remove unnecessary lazy-seq call

[tomdl89]

Just noticed as I was checking the source code, that partition-between calls lazy-seq twice in a row (well, with a letfn binding form between them, but that doesn't matter), which is unnecessary. All tests still pass without it, as would be expected. Low priority, no doubt, but worth tidying up I guess.

[weavejester]

Thanks for the patch! Sorry this took so long to merge.