Removing unused #include aos/once.h

Change-Id: Id721b2b631a316725eecd8a97600eb4fca8b5b47
diff --git a/y2018/BUILD b/y2018/BUILD
index fc2aae8..d7cc2fd 100644
--- a/y2018/BUILD
+++ b/y2018/BUILD
@@ -49,7 +49,6 @@
     ],
     visibility = ["//visibility:public"],
     deps = [
-        "//aos:once",
         "//aos/logging",
         "//aos/mutex",
         "//aos/network:team_number",
diff --git a/y2018/constants.cc b/y2018/constants.cc
index 97a62a1..ea21a5b 100644
--- a/y2018/constants.cc
+++ b/y2018/constants.cc
@@ -13,7 +13,6 @@
 #include "aos/logging/logging.h"
 #include "aos/mutex/mutex.h"
 #include "aos/network/team_number.h"
-#include "aos/once.h"
 
 #include "y2018/control_loops/drivetrain/drivetrain_dog_motor_plant.h"
 #include "y2018/control_loops/drivetrain/polydrivetrain_dog_motor_plant.h"