Remove duplicate definitions (#8483)

stdlib/_markupbase.pyi

@@ -2,7 +2,6 @@ import sys
 from typing import Any
 
 class ParserBase:
-    def __init__(self) -> None: ...
     def reset(self) -> None: ...
     def getpos(self) -> tuple[int, int]: ...
     def unknown_decl(self, data: str) -> None: ...