Pull state out of the zeroing estimators more nicely

I'm eventually going to remove the position() member, but for now Austin
wants this too.

Change-Id: I12b0c01eb5174751bd04fee8fdb770378a87f541
diff --git a/frc971/control_loops/profiled_subsystem.h b/frc971/control_loops/profiled_subsystem.h
index 9a19201..45ef912 100644
--- a/frc971/control_loops/profiled_subsystem.h
+++ b/frc971/control_loops/profiled_subsystem.h
@@ -98,11 +98,7 @@
 
   // Returns the current internal estimator state for logging.
   typename ZeroingEstimator::State EstimatorState(int index) {
-    typename ZeroingEstimator::State estimator_state;
-    ::frc971::zeroing::PopulateEstimatorState(estimators_[index],
-                                              &estimator_state);
-
-    return estimator_state;
+    return estimators_[index].GetEstimatorState();
   }
 
   // Sets the maximum voltage that will be commanded by the loop.