Relicense shootout-k-nucleotide.rs

Everyone agreed except @thestinger. As @thestinger contribution on this file is trivial,
we can relicense it.

Related to #14248, close #15330
auto merge of #16006 : TeXitoi/rust/relicense-shootout-k-nucleotide, r=brson

Everyone agreed except @thestinger. As @thestinger contribution on this file is trivial,
we can relicense it.

Related to #14248, close #15330

@brson OK?