Noiseless IMU fix

[plusk01]

Fixed what seems to be a copy/paste error.

I noticed that setting noise_on to false in my agent's yaml (as below), the accelerometer bias was still non-zero

# IMU
imu: {
  noise_on: false,
  topic: imu/data,
  rate: 500,
  gyro_bias_topic: imu/gyro_bias,
  gyro_stdev: 0.005,
  gyro_bias_range: 0.005,
  gyro_bias_walk_stdev: 0.0001,
  acc_bias_topic: imu/acc_bias,
  acc_stdev: 0.05,
  acc_bias_range: 0.01,
  acc_bias_walk_stdev: 0.0001
}

FYI @skyler237 @jerelbn @superjax @gellings