Split logger.h into log_reader and log_writer

Much simpler!

Change-Id: I6c4ee363b56b67dac40c456261bbed79d01b8eb6
diff --git a/frc971/control_loops/drivetrain/BUILD b/frc971/control_loops/drivetrain/BUILD
index ad39bcf..8c3274d 100644
--- a/frc971/control_loops/drivetrain/BUILD
+++ b/frc971/control_loops/drivetrain/BUILD
@@ -470,7 +470,7 @@
         ":drivetrain_output_fbs",
         ":drivetrain_test_lib",
         "//aos/controls:control_loop_test",
-        "//aos/events/logging:logger",
+        "//aos/events/logging:log_writer",
         "//aos/testing:googletest",
         "//frc971/queues:gyro_fbs",
         "//frc971/wpilib:imu_fbs",