Remove direct dependence of beam-sqlite on platform-specific packages

[LaurentRDC]

This PR removes beam-sqlite's direct dependence on either the unix or windows package, which should allow to build beam-core and beam-sqlite on a wider variety of platforms.

Fixes #738

Before merging, I want to at least manually check that beam-sqlite can be compiled using the WASM backend

[dhess]

Thanks for the remarkably quick turnaround on this request!

We haven't yet properly integrated beam-sqlite into our project, but I quickly added it to our project's deps so that it gets built, and I can confirm that this branch builds with the Wasm backend, using the latest version of these tools: https://gitlab.haskell.org/haskell-wasm/ghc-wasm-meta

[LaurentRDC]

Thanks for checking! I released a new version of beam-sqlite on Hackage

[dhess]

Amazing, thank you!