bpo-38605: Revert making 'from __future__ import annotations' the default (GH-25490)

This reverts commits 044a1048ca93d466965afc027b91a5a9eb9ce23c and 1be456ae9d53bb1cba2b24fc86175c282d1c2169, adapting the code to changes that happened after it.
diff --git a/Lib/test/dataclass_textanno.py b/Lib/test/dataclass_textanno.py
index 589b60f..3eb6c94 100644
--- a/Lib/test/dataclass_textanno.py
+++ b/Lib/test/dataclass_textanno.py
@@ -1,3 +1,5 @@
+from __future__ import annotations
+
 import dataclasses