Group commands by topic in “pysetup run --list-commands” output.

This fixes a regression from distutils, where “setup.py --help-commands”
prints out commands grouped by topic (i.e. building vs. installing),
which is more useful than using sorted.
diff --git a/Lib/packaging/run.py b/Lib/packaging/run.py
index 4756f7c..c3600a7 100644
--- a/Lib/packaging/run.py
+++ b/Lib/packaging/run.py
@@ -254,16 +254,13 @@
     parser = dispatcher.parser
     args = args[1:]
 
-    commands = STANDARD_COMMANDS  # + extra commands
+    commands = STANDARD_COMMANDS  # FIXME display extra commands
 
     if args == ['--list-commands']:
         print('List of available commands:')
-        cmds = sorted(commands)
-
-        for cmd in cmds:
+        for cmd in commands:
             cls = dispatcher.cmdclass.get(cmd) or get_command_class(cmd)
-            desc = getattr(cls, 'description',
-                            '(no description available)')
+            desc = getattr(cls, 'description', '(no description available)')
             print('  %s: %s' % (cmd, desc))
         return