update the information about enabled vs not

With the roboRIO, we get different information about whether motors are
enabled (and some about sensors too), so the system for propagating it
around to everything needs to change.

Change-Id: I7e5f9591eeac1fdfe57b271333c3827431fbef01
diff --git a/frc971/wpilib/gyro_sender.cc b/frc971/wpilib/gyro_sender.cc
index a155b7e..0ea2236 100644
--- a/frc971/wpilib/gyro_sender.cc
+++ b/frc971/wpilib/gyro_sender.cc
@@ -116,8 +116,8 @@
         have_zeroing_data = true;
       }
 
-      ::aos::robot_state.FetchLatest();
-      if (::aos::robot_state.get() && ::aos::robot_state->enabled &&
+      ::aos::joystick_state.FetchLatest();
+      if (::aos::joystick_state.get() && ::aos::joystick_state->enabled &&
           have_zeroing_data) {
         zero_offset = 0;
         for (size_t i = 0; i < sizeof(zeroing_data) / sizeof(zeroing_data[0]);