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/test_opcodes.py b/Lib/test/test_opcodes.py
index 4be78a4..d43a830 100644
--- a/Lib/test/test_opcodes.py
+++ b/Lib/test/test_opcodes.py
@@ -39,7 +39,7 @@ class C: pass
     def test_use_existing_annotations(self):
         ns = {'__annotations__': {1: 2}}
         exec('x: int', ns)
-        self.assertEqual(ns['__annotations__'], {'x': 'int', 1: 2})
+        self.assertEqual(ns['__annotations__'], {'x': int, 1: 2})
 
     def test_do_not_recreate_annotations(self):
         # Don't rely on the existence of the '__annotations__' global.