fix(OpenSRP Deduplicator): Multiple fixes (#5681)

**Story card:**
[sc-16598](https://app.shortcut.com/simpledotorg/story/16598/fix-import-api-duplications)

## Because

We noticed some bugs while testing this

## This addresses

- **do nothing if the old_entity is nil i.e. already merged**
- **only merge medical histories when both are present**
- **fix associated deduplicator calls**
- **discard patients**

## Test instructions

n/a

Author: igbanam

app/services/one_off/opensrp/deduplicator.rb

@@ -74,7 +74,7 @@ def call!
 
       def deprecate_old_patients
         @old_patients = @duplicates.map(&:first)
-        Patient.where(id: @old_patients).discard!
+        Patient.where(id: @old_patients).map(&:discard!)
       end
 
       private

app/services/one_off/opensrp/deduplicators/for_entity.rb

@@ -2,8 +2,12 @@ module OneOff
   module Opensrp
     module Deduplicators
       class ForEntity
-        def self.call! old_id, new_id
-          new(old_id, new_id).call
+        def self.call! old_id, new_id, assoc = nil
+          if assoc.nil?
+            new(old_id, new_id).call!
+          else
+            new(old_id, new_id, assoc).call!
+          end
         end
 
         def initialize old_id, new_id

app/services/one_off/opensrp/deduplicators/for_immutable_entity.rb

@@ -9,7 +9,7 @@ def initialize old_id, new_id, assoc = nil
         end
 
         def merge
-          old_patient.send(assoc).each do |associated|
+          old_patient.send(@association).each do |associated|
             associated.patient = new_patient
             associated.save!
           end

app/services/one_off/opensrp/deduplicators/for_medical_history.rb

@@ -23,10 +23,18 @@ class ForMedicalHistory < ForMutableEntity
         ].freeze
 
         def merge
-          new_patient.medical_history.tap do |new_medical_history|
-            merge_old(new_medical_history, old_patient.medical_history, CHOOSING_OLD)
-            merge_new(new_medical_history, old_patient.medical_history, CHOOSING_NEW)
+          if new_patient.medical_history.nil?
+            new_patient.medical_history = old_patient.medical_history
+            new_patient.save!
+            old_patient.medical_history.discard!
+          else
+            new_patient.medical_history.tap do |new_medical_history|
+              merge_old(new_medical_history, old_patient.medical_history, CHOOSING_OLD)
+              merge_new(new_medical_history, old_patient.medical_history, CHOOSING_NEW)
+            end
           end
+
+          new_patient.medical_history
         end
       end
     end

app/services/one_off/opensrp/deduplicators/for_mutable_entity.rb

@@ -22,6 +22,7 @@ def merge_new(entity, old_patient, attributes)
         end
 
         def merge_old(entity, old_entity, attributes)
+          return if old_entity.nil?
           attributes.each do |attr|
             entity.send("#{attr}=", old_entity.send(attr))
           end