Fix rounding issue in OUSD redeemAll unit test

To get the unit test passing, the last assertion in the redeemAll unit tests has been commented out. This issue is to get to the bottom of the following error.

  1) Vault Redeem
       Should have redeemAll result in zero balance:

      AssertionError: Expected "1" to be equal 0
      + expected - actual

       {
      -  "_hex": "0x00"
      +  "_hex": "0x01"
         "_isBigNumber": true
       }
      
      at Proxy.<anonymous> (test/helpers.js:56:28)
      at processTicksAndRejections (node:internal/process/task_queues:95:5)
      at runNextTicks (node:internal/process/task_queues:64:3)
      at listOnTimeout (node:internal/timers:538:9)
      at processTimers (node:internal/timers:512:7)
      at Context.<anonymous> (test/vault/redeem.js:431:5)

Start with test/vault/redeem.js around line 431 and inspect the assertion helper at test/helpers.js:56. Run the redeemAll unit test and trace why the final balance is 1 instead of 0. Done means the underlying rounding issue is addressed and the final assertion can be restored and passes.