Switch to I18n::Backend::Simple.new due to i18n-js compatibility

[kennyadsl]

This will fix fnando/i18n-js#344

[jhawthorn]

Is it possible to remove this file entirely? I don't think we should be doing what it does, and it seems like setting I18n.backend = I18n::Backend::Simple.new would bypass its functionality entirely anyways.

[kennyadsl]

👍 We can probably revert this whole commit: 1bec159. I think i18n_data would be useless as well.

[jhawthorn]

I think unfortunately this is being used by BaseHelper's available_countries. I still want to remove this file but I think we need to find another way to get translated country names.

[jhawthorn]

Amusingly, this doesn't check the scope of the translation:

I18n.t('CA', scope: 'foo.bar.baz') #=> "Canada"

[jhawthorn]

#2537 solves this and is ready to go, but I'm not sure how to handle this version-wise.

If we remove this initializer we'll be dropping support for translating countries in all versions < 2.5. Maybe we need a major version bump, to make this solidus_i18n 2.0.

[kennyadsl]

I've prepared a PR (#108) to remove this dependency if we go for the major version bump.

Alternatively we could leave the initializer and conditionally load that code only for some solidus version using this check?

[jhawthorn]

Solved by #122 🎉