Akuli and srittau: Remove Python 2 branches from Python 3 stubs (#5461)

* run script and do some manual changes (Akuli)

* do the whole thing manually (srittau)

* merge changes (Akuli)

Co-authored-by: Sebastian Rittau <srittau@rittau.biz>

stdlib/rlcompleter.pyi

@@ -1,10 +1,6 @@
-import sys
-from typing import Any, Dict, Optional, Union
+from typing import Any, Dict, Optional
 
-if sys.version_info >= (3,):
-    _Text = str
-else:
-    _Text = Union[str, unicode]
+_Text = str
 
 class Completer:
     def __init__(self, namespace: Optional[Dict[str, Any]] = ...) -> None: ...