Bump i18n-js to latest prerelease

User Story # 15318

Signed-off-by: Alex Coles <alex@alexbcoles.com>
Correct configuration for i18n-js w/asset pipeline

`I18n::JS::Middleware` is only necessary if we're not using the Rails
asset pipeline.

See https://github.com/fnando/i18n-js#rails-app-with-asset-pipeline

If we migrate away from the asset pipeline, this commit should be
reverted.

Signed-off-by: Alex Coles <alex@alexbcoles.com>
Remove erroneously committed translations file

Signed-off-by: Alex Coles <alex@alexbcoles.com>
Remove redundant I18nJsHelper

Signed-off-by: Alex Coles <alex@alexbcoles.com>
Merge pull request #1821 from opf/feature/update-i18n-js

15318 Upgrade i18n-js, removing redundant config