Bug 1628838 - Fix mach python on Windows by unsetting PYTHONUNBUFFERED. r=glandium

The existence of this environment variable breaks the Python shell on Windows, so make sure it's unset (but only in this case to avoid regressing bug 1627873).

Differential Revision: https://phabricator.services.mozilla.com/D70542

python/mach_commands.py

@@ -87,6 +87,7 @@ class MachCommands(MachCommandBase):
         return self.run_process([python_path] + args,
                                 pass_thru=True,  # Allow user to run Python interactively.
                                 ensure_exit_code=False,  # Don't throw on non-zero exit code.
+                                python_unbuffered=False,  # Leave input buffered.
                                 append_env=append_env)
 
     @Command('python-test', category='testing',