Refactor PatientMerger to use PatientDeleter

Jira-Issue: MAV-7067

Author: alistair-white-horne-tng

app/lib/patient_merger.rb

@@ -181,7 +181,7 @@ def call
         user: @user
       )
 
-      patient_to_destroy.reload.destroy!
+      PatientDeleter.call(patients: Patient.where(id: patient_to_destroy.id))
 
       PatientStatusUpdater.call(patient: patient_to_keep)
     end

spec/models/patient_spec.rb

@@ -1446,36 +1446,6 @@
     end
   end
 
-  describe "#destroy_childless_parents" do
-    context "when parent has only one child" do
-      let(:parent) { create(:parent) }
-      let!(:patient) { create(:patient, parents: [parent]) }
-
-      it "destroys the parent when the patient is destroyed" do
-        expect { patient.destroy }.to change(Parent, :count).by(-1)
-      end
-    end
-
-    context "when parent has multiple children" do
-      let(:parent) { create(:parent) }
-      let!(:patient) { create(:patient, parents: [parent]) }
-
-      before { create(:patient, parents: [parent]) }
-
-      it "does not destroy the parent when one patient is destroyed" do
-        expect { patient.destroy }.not_to change(Parent, :count)
-      end
-    end
-
-    context "when patient has multiple parents" do
-      let!(:patient) { create(:patient, parents: create_list(:parent, 2)) }
-
-      it "destroys only the childless parents" do
-        expect { patient.destroy }.to change(Parent, :count).by(-2)
-      end
-    end
-  end
-
   describe "#latest_pds_search_result" do
     subject(:latest_pds_search_result) { patient.latest_pds_search_result }