[Update] gym-pybullet-drones example

Author: wenzhangliu

examples/drones/demo_drones.py

@@ -26,7 +26,4 @@ def parse_args():
                         env=parser.env,
                         env_id=parser.env_id,
                         parser_args=parser)
-    if parser.benchmark:
-        runner.run(mode='benchmark')
-    else:
-        runner.run(mode='train')
+    runner.run(mode='benchmark')