[Bug] Clean up WorkersToDelete after the scaling process finishes

[kevin85421]

Why are these changes needed?

• Delete "should update a raycluster object deleting a random pod".

  • In [release blocker][Feature] Only Autoscaler can make decisions to delete Pods #1253, we decided to make Ray Autoscaler the only decision maker to delete Ray Pods. In the test, random Pod deletion will not happen because EnableInTreeAutoscaling is true.

• The test "simulate Ray Autoscaler scales down" simulates the Ray Autoscaler's behavior to scale down the RayCluster by updating WorkersToDelete. However, we don't clean up the WorkersToDelete after the scaling process finishes.

Related issue number

Checks

• I've made sure the tests are passing.
• Testing Strategy
  • Unit tests
  • Manual tests
  • This PR is not tested :(