Update cbioportalImporter.py

[DheerajRawandhe]

What this PR does

Fixes an issue where deleting samples could leave patients with no samples.

Problem

The remove-samples command removed only samples, but not patients.
This created "sample-less" patients, which can break API or UI.

Fix

After deleting samples:

• Check patients linked to those samples
• If a patient has 0 samples left → delete that patient too

Result

• No invalid patients in DB
• Data stays clean and consistent

Test

• Deleted last sample of a patient → patient also deleted
• Deleted some samples → patient still exists

[sheridancbio]

I believe we want to support studies which contain patients which have no samples. Others should comment --- does this break the API or frontend? If we want to support instances of patients with no samples perhaps the API implementations and frontend logic must be fixed.