Remove usage of CHECK_NOTNULL

We want to switch to absl logging instead of glog.  gtest and ceres are
going there, and we already have absl as a dependency.  ABSL doesn't
have CHECK_NOTNULL, and we can move things over in an easier to review
fashion.

Change-Id: Ifd9a11ec34a2357cec43f88dba015db9c28ed2cf
Signed-off-by: Austin Schuh <austin.linux@gmail.com>
diff --git a/y2024/control_loops/drivetrain/drivetrain_base.cc b/y2024/control_loops/drivetrain/drivetrain_base.cc
index 79d35e1..dd4f33c 100644
--- a/y2024/control_loops/drivetrain/drivetrain_base.cc
+++ b/y2024/control_loops/drivetrain/drivetrain_base.cc
@@ -11,9 +11,10 @@
 const frc971::control_loops::drivetrain::DrivetrainConfig<double>
 GetDrivetrainConfig(aos::EventLoop *event_loop) {
   frc971::constants::ConstantsFetcher<Constants> constants_fetcher(event_loop);
+  CHECK(constants_fetcher.constants().common() != nullptr);
+  CHECK(constants_fetcher.constants().common()->drivetrain() != nullptr);
   return frc971::control_loops::drivetrain::DrivetrainConfig<double>::
-      FromFlatbuffer(
-          *CHECK_NOTNULL(constants_fetcher.constants().common()->drivetrain()));
+      FromFlatbuffer(*constants_fetcher.constants().common()->drivetrain());
 };
 
 }  // namespace y2024::control_loops::drivetrain
diff --git a/y2024/control_loops/superstructure/aiming.cc b/y2024/control_loops/superstructure/aiming.cc
index d8d336f..b53dbb5 100644
--- a/y2024/control_loops/superstructure/aiming.cc
+++ b/y2024/control_loops/superstructure/aiming.cc
@@ -11,7 +11,10 @@
 Aimer::Aimer(aos::EventLoop *event_loop,
              const y2024::Constants *robot_constants)
     : event_loop_(event_loop),
-      robot_constants_(CHECK_NOTNULL(robot_constants)),
+      robot_constants_([&]() {
+        CHECK(robot_constants != nullptr);
+        return robot_constants;
+      }()),
       drivetrain_config_(
           frc971::control_loops::drivetrain::DrivetrainConfig<double>::
               FromFlatbuffer(*robot_constants_->common()->drivetrain())),
@@ -58,7 +61,7 @@
   } else {
     received_joystick_state_ = true;
 
-    CHECK_NOTNULL(joystick_state_fetcher_.get());
+    CHECK(joystick_state_fetcher_.get() != nullptr);
     alliance = joystick_state_fetcher_->alliance();
   }
 
diff --git a/y2024/control_loops/superstructure/superstructure.cc b/y2024/control_loops/superstructure/superstructure.cc
index a485943..7f7da4f 100644
--- a/y2024/control_loops/superstructure/superstructure.cc
+++ b/y2024/control_loops/superstructure/superstructure.cc
@@ -36,7 +36,7 @@
     : frc971::controls::ControlLoop<Goal, Position, Status, Output>(event_loop,
                                                                     name),
       constants_fetcher_(event_loop),
-      robot_constants_(CHECK_NOTNULL(&constants_fetcher_.constants())),
+      robot_constants_(&constants_fetcher_.constants()),
       drivetrain_status_fetcher_(
           event_loop->MakeFetcher<frc971::control_loops::drivetrain::Status>(
               "/drivetrain")),
diff --git a/y2024/control_loops/superstructure/superstructure_lib_test.cc b/y2024/control_loops/superstructure/superstructure_lib_test.cc
index 59398ab..719a29b 100644
--- a/y2024/control_loops/superstructure/superstructure_lib_test.cc
+++ b/y2024/control_loops/superstructure/superstructure_lib_test.cc
@@ -312,8 +312,7 @@
         superstructure_(superstructure_event_loop.get()),
         test_event_loop_(MakeEventLoop("test", roborio_)),
         constants_fetcher_(test_event_loop_.get()),
-        simulated_robot_constants_(
-            CHECK_NOTNULL(&constants_fetcher_.constants())),
+        simulated_robot_constants_(&constants_fetcher_.constants()),
         superstructure_goal_fetcher_(
             test_event_loop_->MakeFetcher<Goal>("/superstructure")),
         superstructure_goal_sender_(