Fold y2019 localizer into drivetrain

Change-Id: Icc192ae9f910741b54f114ec9a27559cc289b29b
diff --git a/frc971/control_loops/drivetrain/drivetrain.cc b/frc971/control_loops/drivetrain/drivetrain.cc
index 9cf71f7..19e604d 100644
--- a/frc971/control_loops/drivetrain/drivetrain.cc
+++ b/frc971/control_loops/drivetrain/drivetrain.cc
@@ -231,6 +231,8 @@
     Y << position->left_encoder, position->right_encoder, last_gyro_rate_,
         last_accel_;
     kf_.Correct(Y);
+    // TODO(james): Account for delayed_U as appropriate (should be
+    // last_last_*_voltage).
     localizer_->Update({last_left_voltage_, last_right_voltage_}, monotonic_now,
                        position->left_encoder, position->right_encoder,
                        last_gyro_rate_, last_accel_);