We have a lot of verbose headers, and i think now is the best opportunity we have to become reuse compliant given that we just did two other similar maintenance changes (prettier, typescirpt5 & eslint9 & typescript-eslint).
* synapse_antispam resuse headers.
* delete old unused tslint.json.
* Add REUSE to pre-commit config.
* reuse info for config directory.
