Remove old store file post-refactor

[jarmoza]

During the refactor I wanted the old store version to stick around as an example in case we missed something during our design of the new store.

Once the store refactor is done (ostensibly with Phase 2), the previous store, now named index-old.js should be removed from the repo.

[github-actions]

We want to keep our issues up to date and active. This issue hasn't seen any activity in the last 30 days.
We have applied the stale-issue label to indicate that this issue should be reviewed again and then either prioritized or closed.

[surchs]

@jarmoza: is this blocked? If so, could you move it to "tracked" in the new status?

[jarmoza]

This is "Next", so I marked it as "Specify - Done".

[jarmoza]

Closed by #383