Revert "fix: optional type var for Resource with python 3.13+"

This reverts commit ef3e523.

Author: azmeuk

scim2_models/resources/resource.py

@@ -1,4 +1,3 @@
-import sys
 from datetime import datetime
 from typing import TYPE_CHECKING
 from typing import Annotated
@@ -103,11 +102,7 @@ def from_schema(cls, schema: "Schema") -> type["Extension"]:
         return _make_python_model(schema, cls)
 
 
-# TypeVar with default parameter is available in Python 3.13+
-if sys.version_info >= (3, 13):
-    AnyExtension = TypeVar("AnyExtension", bound="Extension", default="Extension")
-else:  # pragma: no cover
-    AnyExtension = TypeVar("AnyExtension", bound="Extension")
+AnyExtension = TypeVar("AnyExtension", bound="Extension")
 
 _PARAMETERIZED_CLASSES: dict[tuple[type, tuple[Any, ...]], type] = {}