Drop __post_serialize__ from SourceDefinition node class

The method `__post_serialize__` on the `SourceDefinition` was used for
ensuring the property `_event_status` didn't make it to the serialized
version of the node. Now that resource definition of `SourceDefinition`
handles serialization/deserialization, we can drop `__post_serialize__`
as it is no longer needed.

core/dbt/contracts/graph/nodes.py

@@ -1230,11 +1230,6 @@ class SourceDefinition(
     def resource_class(cls) -> Type[SourceDefinitionResource]:
         return SourceDefinitionResource
 
-    def __post_serialize__(self, dct):
-        if "_event_status" in dct:
-            del dct["_event_status"]
-        return dct
-
     def same_database_representation(self, other: "SourceDefinition") -> bool:
         return (
             self.database == other.database

tests/unit/test_contracts_graph_parsed.py

@@ -50,6 +50,7 @@
     TestMetadata,
     SemanticModel,
 )
+from dbt.artifacts.resources import SourceDefinition as SourceDefinitionResource
 from dbt import flags
 from argparse import Namespace
 
@@ -2036,13 +2037,13 @@ def test_basic_source_definition(
     node_dict = basic_parsed_source_definition_dict
     minimum = minimum_parsed_source_definition_dict
 
-    assert_symmetric(node, node_dict, SourceDefinition)
+    assert_symmetric(node.to_resource(), node_dict, SourceDefinitionResource)
 
     assert node.is_ephemeral is False
     assert node.is_refable is False
     assert node.has_freshness is False
 
-    assert_from_dict(node, minimum, SourceDefinition)
+    assert_from_dict(node.to_resource(), minimum, SourceDefinitionResource)
     pickle.loads(pickle.dumps(node))
 
 
@@ -2063,7 +2064,7 @@ def test_complex_source_definition(
 ):
     node = complex_parsed_source_definition_object
     node_dict = complex_parsed_source_definition_dict
-    assert_symmetric(node, node_dict, SourceDefinition)
+    assert_symmetric(node.to_resource(), node_dict, SourceDefinitionResource)
 
     assert node.is_ephemeral is False
     assert node.is_refable is False