Remove stream_data from the cluster.

[showell]

[timabbott]

Thanks for working on this @showell! I posted a batch of comments; otherwise lgtm.

[showell]

The first two commits here should be no-brainers to merge (just node test cleanup). And the third can probably also be merged (since no comments on it).

[timabbott]

(Merged the first two; https://github.com/zulip/zulip/pull/18193#discussion_r615143892 is about the third).

[showell]

(rebased off of latest master)

[zulipbot]

Heads up @showell, we just merged some commits that conflict with the changes your made in this pull request! You can review this repository's recent commits to see where the conflicts occur. Please rebase your feature branch against the upstream/main branch and resolve your pull request's merge conflicts accordingly.