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/y2023_bot3/wpilib_interface.cc b/y2023_bot3/wpilib_interface.cc
index 1dd8efd..1f0c003 100644
--- a/y2023_bot3/wpilib_interface.cc
+++ b/y2023_bot3/wpilib_interface.cc
@@ -113,7 +113,7 @@
     // device temp is not timesynced so don't add it to the list of signals
     device_temp_.SetUpdateFrequency(kCANUpdateFreqHz);
 
-    CHECK_NOTNULL(signals);
+    CHECK(signals != nullptr);
 
     supply_voltage_.SetUpdateFrequency(kCANUpdateFreqHz);
     signals->push_back(&supply_voltage_);