upload-file: Remove ancient StringIO workaround.

Signed-off-by: Anders Kaseorg <[email protected]>

Author: andersk

zulip/zulip/examples/upload-file

@@ -1,16 +1,11 @@
 #!/usr/bin/env python3
 
 import argparse
-from io import StringIO as _StringIO
+from io import StringIO
 from typing import IO, Any
 
 import zulip
 
-
-class StringIO(_StringIO):
-    name = ""  # https://github.com/python/typeshed/issues/598
-
-
 usage = """upload-file [options]
 
 Upload a file, and print the corresponding URI.