Delete purge_ttl.rs

[data-sync-user]

We never put the Rust based purge_ttl.rs script into production. The original goal was to rewrite it in Rust to avoid the need for any Python in the final docker image.

Successful purge runs of our large Spanner instance turned out to be trickier than we originally thought, so working alongside SRE we revamped the Python version, quickly prototyping a number of different iterations of it splitting the job into smaller more manageable chunks (since we were on a tight schedule).

In the meantime Python has become standard in our docker and won’t be going away any time soon, particularly with the addition of tokenserver. Let’s nuke this Rust script as it’s beginning to get out of date with the spanner implementation (e.g. https://mozilla-hub.atlassian.net/browse/SYNC-3922 )

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