[2.9] plugin_formatter: sys.exit does not take a file argument

Cleanup of leftover from bcdfdc0cc3.

sys.exit does not take any named argument.

(cherry picked from commit cdad594b16)

hacking/build_library/build_ansible/command_plugins/plugin_formatter.py

@@ -678,9 +678,9 @@ def validate_options(options):
     ''' validate option parser options '''
 
     if not options.module_dir:
-        sys.exit("--module-dir is required", file=sys.stderr)
+        sys.exit("--module-dir is required")
     if not os.path.exists(options.module_dir):
-        sys.exit("--module-dir does not exist: %s" % options.module_dir, file=sys.stderr)
+        sys.exit("--module-dir does not exist: %s" % options.module_dir)
     if not options.template_dir:
         sys.exit("--template-dir must be specified")