Packaging cleanup: normalize print calls.

Namely: use default arguments instead of explicit empty string; use multiple
arguments instead of building strings.
diff --git a/Lib/packaging/dist.py b/Lib/packaging/dist.py
index 6065e78..5c390ce 100644
--- a/Lib/packaging/dist.py
+++ b/Lib/packaging/dist.py
@@ -509,14 +509,14 @@
                 options = self.global_options
             parser.set_option_table(options)
             parser.print_help(self.common_usage + "\nGlobal options:")
-            print('')
+            print()
 
         if display_options:
             parser.set_option_table(self.display_options)
             parser.print_help(
                 "Information display options (just display " +
                 "information, ignore any commands)")
-            print('')
+            print()
 
         for command in self.commands:
             if isinstance(command, type) and issubclass(command, Command):
@@ -529,7 +529,7 @@
             else:
                 parser.set_option_table(cls.user_options)
             parser.print_help("Options for %r command:" % cls.__name__)
-            print('')
+            print()
 
         print(gen_usage(self.script_name))
 
@@ -544,7 +544,7 @@
         # we ignore "foo bar").
         if self.help_commands:
             self.print_commands()
-            print('')
+            print()
             print(gen_usage(self.script_name))
             return 1