Remove pre-print and collaboration terms from challenge DUA/license

[tompollard]

@priyankchokshi05-sudo has pointed out that there some unhelpful terms in one of the challenge licenses/DUAs:

11. The LICENSEE will not post preprints of their work and/or post the data on any public machine/site, or share the data privately with non-team members.
12. The LICENSEE will not work with any other team that enters the Challenge or intends to enter the Challenge.

MIT-LCP/license-and-dua@fca9883#commitcomment-186657005