Investigate removing the `waitingloan` table

### Problem

As @cdrini identified in https://github.com/internetarchive/openlibrary/pull/9404, the `waitingloan` table might be unused now that `/admin/waitinglist` has been removed.

### Proposal & Constraints

Verify if this is the case, and remove the `waitingloan` table and all associated code if so.

### Leads

### Related files

### Stakeholders
@cdrini

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