Using --purge-days with gdrive storage

Seems to have no effect with using purge-days and purge-interval while using gdrive as provider.
Files remain untouched since created date. Been 3 days.
Theres no instance of anything in logs either that it ran or failed, is this feature only for local storage?

```nohup go run main.go --tls-listener 192.168.50.249:443 --purge-days 1 --purge-interval 1 --provider gdrive --basedir transfers --gdrive-client-json-filepath ./cred/oauth.json --gdrive-local-config-path ./cred/ --web-path ../transfer.sh-web/dist/ --force-https --tls-cert-file ../transfer.sh-web/cert.pem --tls-private-key ../transfer.sh-web/key.pem --log ./log.txt --max-upload-size 1048576```

Start in main.go by tracing --purge-days and --purge-interval with the gdrive provider, then reproduce the supplied command and inspect the configured log file. Done means the purge behavior is corrected for gdrive or the issue clearly documents that this provider does not support it, with a test or reproducible result.

Written by the indexing model from the issue text.