⏪️(backend) remove is_main default hack

As DRF encode/django-rest-framework#9030 has
been reverted in 3.15.1, the related hack is no longer needed.

src/backend/joanie/core/serializers/client.py

@@ -8,7 +8,6 @@
 import markdown
 from drf_spectacular.utils import extend_schema_field
 from rest_framework import exceptions, serializers
-from rest_framework.fields import empty
 from rest_framework.generics import get_object_or_404
 
 from joanie.core import enums, models
@@ -86,15 +85,6 @@ class Meta:
             "id",
         ]
 
-    def run_validation(self, data=empty):
-        """
-        Ignore is_main if not present in the data
-        """
-        validated_data = super().run_validation(data)
-        if "is_main" not in data:
-            del validated_data["is_main"]
-        return validated_data
-
 
 class CourseLightSerializer(AbilitiesModelSerializer):
     """

src/backend/joanie/payment/serializers.py

@@ -1,7 +1,6 @@
 """Serializers for api."""
 
 from rest_framework import serializers
-from rest_framework.fields import empty
 
 from joanie.payment import models
 
@@ -31,12 +30,3 @@ class Meta:
             "expiration_year",
             "last_numbers",
         ]
-
-    def run_validation(self, data=empty):
-        """
-        Ignore is_main if not present in the data
-        """
-        validated_data = super().run_validation(data)
-        if "is_main" not in data:
-            del validated_data["is_main"]
-        return validated_data