Database benchmarks do not typecheck

[dhil]

@jamescheney the programs under the directory database/ (formerly benchmarks/ on links-lang/links) do not type check. I suppose these programs served as benchmarks for some paper once a upon time. Are you interested in keeping them? If so, we should either bring them up to date or pin them to the Links version they used to work with.

[jamescheney]

These are from the SIGMOD 2014 paper and also used in @fehrenbach's thesis work/papers. The type errors are probably due to the changes we made to query typechecking last year and should be easy to correct.