avocado.plugins.runner: Remove unnecessary print_help().

The code seems to be dead (ineffective) at this part, since argparse
already checks previously if the url argument is passed.
Signed-off-by: NRudá Moura <rmoura@redhat.com>

avocado/plugins/runner.py

@@ -139,7 +139,4 @@ class TestRunner(plugin.Plugin):
 
         job_instance = job.Job(args)
         rc = job_instance.run()
-        if not args.url:
-            self.parser.print_help()
-
         return rc