Remove deprecated email list exporter

[zwolf]

Previous use of mailout1 email server (running X, hosted on linode) made use of CSV exports of email lists. Even after migration from AWS to Azure, we continued to export lists to secure S3 buckets. Previously this issue was focused on updating the panoptes email list exports uploader to use the azure media storage adapter (move away from S3; see S3 specific code here.

Now, in the listmonk era where list syncing is performed by https://github.com/zooniverse/listmonk-sync, there is no need to run these email list exports.

Proposed action: halt daily export job (sidekiq cron job) and remove s3 export code (optional, but probably good move to remove aws cli dependencies?)