trust_server_pasv_ipv4_address: move comments to allowlists (#6496)

Co-authored-by: Jelle Zijlstra <jelle.zijlstra@gmail.com>

stdlib/ftplib.pyi

@@ -33,10 +33,6 @@ class FTP:
     lastresp: str
     file: TextIO | None
     encoding: str
-
-    # The following variable is intentionally left undocumented.
-    # See https://bugs.python.org/issue43285 for relevant discussion
-    # trust_server_pasv_ipv4_address: bool
     def __enter__(self: Self) -> Self: ...
     def __exit__(
         self, exc_type: Type[BaseException] | None, exc_val: BaseException | None, exc_tb: TracebackType | None