clean python 3 specific stuff from stdlib/@python2 stubs (#5451)

stdlib/@python2/rlcompleter.pyi

@@ -1,10 +1,7 @@
 import sys
 from typing import Any, Dict, Optional, Union
 
-if sys.version_info >= (3,):
-    _Text = str
-else:
-    _Text = Union[str, unicode]
+_Text = Union[str, unicode]
 
 class Completer:
     def __init__(self, namespace: Optional[Dict[str, Any]] = ...) -> None: ...