web: remove unused dependency
web: remove unused dependency

We no longer need elm-http-builder, though we adopt a similar pattern in
the Api module.

Signed-off-by: Aidan Oldershaw <30ef7a6e0d016bc846f26d89dacbd23aceded206@pivotal.io>

concourse/concourse,concourse/concourse,concourse/concourse,concourse/concourse,concourse/concourse