Fix CI failures because of unused names or importing transitive dependencies

[thomashoneyman]

A number of our libraries are failing in CI for one of two reasons:

1. They directly import from a package that isn't explicitly listed as a dependency in their spago.dhall file
2. They contain unused names in their code (ie. an unused function, or an unused argument, or a destructured value that is never used...)

They need to be fixed by taking actions depending on whether they're failing due to the unused names or the transitive dependencies. If you would like to be included in the CHANGELOG you are free to add an entry under the "Other improvements" section (for example: Ensure all imported packages are in the spago.dhall file (#000 by @___)).

Don't bother updating the bower.json files -- I can take care of this later on!

To fix a library that imports from a transitive dependency:

1. Follow the instructions Spago includes about installing missing libraries -- this can basically be copy/pasted into a call to spago install. For example, if Spago reports that a library imports from prelude but doesn't list it as a dependency, then you can fix the issue with spago install prelude.
2. If there are warnings about unused dependencies, then remove the libraries that Spago has identified as unused from the package's spago.dhall file. This has to be done manually -- there is no uninstall command.

To fix a library that has an UnusedName error from the compiler:

1. If the error is reported on a top-level declaration that is unused and not exported, then remove the declaration. (If it should be exported instead, then it will be caught in code review.)
2. If the error is about a declaration that is unused, then remove the declaration.
3. If the error results from destructuring (for example, destructuring a record { a, b } but one or more of the names is unused), then remove the unused names.

When you fix one of these libraries, please include a link to this issue in the pull request so that it automatically shows up on this issue. These libraries need to be fixed:

• nullable (example failure)
• now (example failure)
• matryoshka (example failure)
• js-uri (example failure)
• js-timers (example failure)
• js-date (example failure)
• freet (example failure)
• fork (example failure)
• fixed-points (example failure)
• coroutines (example failure)
• concurrent-queues (example failure)
• avar (example failure)
• argonaut-traversals (example failure)
• argonaut-core (example failure)
• argonaut-codecs (example failure)
• argonaut (example failure)
• affjax (example failure)
• aff-coroutines (example failure)
• aff-bus (example failure)
• aff (example failure)

[pete-murphy]

Seems like there were a few people interested in working on this, not sure what the plan is to coordinate, but FWIW, I'll try my hand at fixing aff (unless anyone's already claimed it 😄) and then see how it goes from there.

[ntwilson]

now is fixed in an earlier PR of mine: https://github.com/purescript-contrib/purescript-now/pull/20/files
I'd be willing to split it into two if that's worthwhile

[pete-murphy]

I'll try to get to affjax, aff-coroutines & aff-bus next

[ntwilson]

I'd love to grab the argonaut family of packages.

[thomashoneyman]

Coordination essentially comes down to checking if there is already a PR or if the library is already checked off 😬 I'm open to ideas for coordination! I'll review and merge things as quickly as I can.

[pete-murphy]

Ah whoops, I didn't think to update the bower.json in any of my PRs, will get to that

[ntwilson]

Is there a good way to check that bower.json got updated correctly (right version numbers, and the correct split between "dependencies" and "devDependencies")?