fix: remove duplicate stream handler (#106)

Author: daniel-sanche

google/cloud/logging_v2/handlers/handlers.py

@@ -139,7 +139,6 @@ def setup_logging(
  logger = logging.getLogger()
  logger.setLevel(log_level)
  logger.addHandler(handler)
- logger.addHandler(logging.StreamHandler())
  for logger_name in all_excluded_loggers:
  logger = logging.getLogger(logger_name)
  logger.propagate = False