Delete tokenserver's decomissioned node entries

[data-sync-user]

Per https://mozilla-hub.atlassian.net/browse/SYNC-4184 :

We can safely delete the old, decommissioned syncstorage nodes stored in tokenserver’s nodes table. The presence of these records shouldn’t cause any issues in theory, but due to their records being invalid in the past (set so during the Spanner migration), they were a root cause of an incident.

Even with those issues fixed (and code added to always force Spanner), we should delete these node entries anyway as they’re no longer needed.

We’ve ensured they’re no longer referenced on production: let’s ensure the same on stage as well, delete them there, and then delete them on production.

┆Issue is synchronized with this Jira Task