Move search table expiration to whenever

[hackartisan]

To those of you with Blacklight apps that run on more than one server and use the blacklight_app role in Princeton Ansible - you may want to consider moving the cron job that the blacklight_app role creates into something generated by Whenever and run it on a single server. This is because Jane and Carolyn found that the cron job running simultaneously on multiple servers is creating database lock errors in postgres, which can cause problems for your application.

Here's a pair of PRs which hopefully resolve this for Orangelight

• Adds the cron job to our "Whenever" configuration on Orangelight, so it runs on only one server
• Removes the blacklight_app role from Orangelight, so that it does not re-create the cron job on all the servers

Thanks to @maxkadel for the report