Remove compatibility aliases (#5464)

* Remove compatibility aliases

Remove a few instances of Text

Use aliases from _typeshed

* Remove unused imports

stdlib/rlcompleter.pyi

@@ -1,7 +1,5 @@
 from typing import Any, Dict, Optional
 
-_Text = str
-
 class Completer:
     def __init__(self, namespace: Optional[Dict[str, Any]] = ...) -> None: ...
-    def complete(self, text: _Text, state: int) -> Optional[str]: ...
+    def complete(self, text: str, state: int) -> Optional[str]: ...