Remove ember-array helper

[kevinhinterlong]

From conversation https://github.com/yahoo/navi/pull/724#discussion_r395671219

This is a legacy helper required from using ember-composable-helpers and relying on the fact that the array helper would return an ember array.

After upgrading ember-composable-helpers to latest, the array helper no longer exists because it's available to all ember apps, however it returns a native array.

We only have one instance of ember-array, so we should remove it and refactor the navi-visualization components that relied on it

[jkusa]

https://github.com/yavin-dev/framework/blob/0a6413a50c14af6cc7867b86fcf39648cb0c68c2/packages/reports/addon/templates/components/report-visualization.hbs#L5