Drop unused private save_m2m flag

docs/topics/release-notes.md

@@ -21,6 +21,8 @@ Major version numbers (x.0.0) are reserved for project milestones.  No major poi
 * Added `PATCH` support.
 * Added `RetrieveUpdateAPIView`.
 * Relation changes are now persisted in `save` instead of in `.restore_object`.
+* Cleanup unused internal `save_m2m` flag on `ModelSerializer.save()`.
+* Relation changes are now persisted in `.save()` instead of in `.restore_object()`.
 * Bugfix: Fix issue with FileField validation with files=None.
 
 ### 2.1.14

rest_framework/serializers.py

@@ -530,13 +530,13 @@ class ModelSerializer(Serializer):
 
         return instance
 
-    def save(self, save_m2m=True):
+    def save(self):
         """
         Save the deserialized object and return it.
         """
         self.object.save()
 
-        if getattr(self, 'm2m_data', None) and save_m2m:
+        if getattr(self, 'm2m_data', None):
             for accessor_name, object_list in self.m2m_data.items():
                 setattr(self.object, accessor_name, object_list)
             self.m2m_data = {}