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/frc971/control_loops/drivetrain/localization/utils.cc b/frc971/control_loops/drivetrain/localization/utils.cc
index c1adb9a..ff6f6c5 100644
--- a/frc971/control_loops/drivetrain/localization/utils.cc
+++ b/frc971/control_loops/drivetrain/localization/utils.cc
@@ -109,7 +109,8 @@
 // verbosity here seems appropriate.
 Eigen::Matrix<double, 4, 4> FlatbufferToTransformationMatrix(
     const frc971::vision::calibration::TransformationMatrix &flatbuffer) {
-  CHECK_EQ(16u, CHECK_NOTNULL(flatbuffer.data())->size());
+  CHECK(flatbuffer.data() != nullptr);
+  CHECK_EQ(16u, flatbuffer.data()->size());
   Eigen::Matrix<double, 4, 4> result;
   result.setIdentity();
   for (int row = 0; row < 4; ++row) {