python: Simplify with str.removeprefix, str.removesuffix.

These are available in Python ≥ 3.9.
https://docs.python.org/3/library/stdtypes.html#str.removeprefix

Signed-off-by: Anders Kaseorg <anders@zulip.com>

scripts/lib/zulip_tools.py

@@ -639,7 +639,7 @@ def get_tornado_ports(config_file: configparser.RawConfigParser) -> list[int]:
             {
                 int(port)
                 for key in config_file.options("tornado_sharding")
-                for port in (key[: -len("_regex")] if key.endswith("_regex") else key).split("_")
+                for port in key.removesuffix("_regex").split("_")
             }
         )
     if not ports: