Fix import details Refs #7073

Gives us a single call site to trigger the destruction of vehicle
journeys, journey patterns, and routes without content.

This was previously done directly in the `#clean` method, but since it's
not needed during referential duplication (only during merges), we don't
want to enable it by default. Thus now to activate the same old
functionality, you would create a `CleanUp` like this:

    CleanUp.new(methods: [:destroy_empty])

Refs #6854

It turns out that we don't care about destroying orphaned data. From
Alban:

> Quand on duplique un JDD, on lance un CleanUp, sauf que la partie
> "suppression des données orphelines" n'intéresse personne au final.

Replace the calls to
`#destory_{vehicle_journeys,journey_patterns,routes}` with one to
`#run_methods`. This change allows callers to run any cleanup methods
defined in `CleanUp`. For example:

    CleanUp.new(methods: [:destory_routes])

But now by default, none of these destroy methods are run, saving us
from doing extra work that it turns out we don't need to bother doing.

Refs #6854

This method is coupled with a new virtual attribute that can be used in
the initializer like:

    CleanUp.new(methods: [:destroy_routes])

The method will run all methods specified in the `:methods` list. The
plan is to replace the calls to `destroy_routes` etc. with a call to
this method. The result will be a more configurable clean-up process,
allowing users to selectively choose what to clean up by declaring what
methods in the `CleanUp` model to call.

Refs #6854