current_bed is not set to None when consultation is discharged

[rithviknishad]

To Reproduce
Steps to reproduce the behavior:

1. Onboard a patient and link a bed that has an Asset Bed with Vitals configured.
2. Observe CNS of that patient.
3. Discharge the patient.
4. Go back to CNS and select show monitors without patient.
5. Observe the same bed, but has that discharged patient show up.
6. This also messes up with newly admitted patients to the same bed.

Expected behavior
set current_bed to None when patient is discharged.