Remove unused, incorrect, duplicate constant

Before I moved the one in //y2017:constants, this was an ODR
violation...

Change-Id: Id44f8a0d72281e8361189ef6977f0de677eb9bbb
diff --git a/y2017/control_loops/drivetrain/drivetrain_base.h b/y2017/control_loops/drivetrain/drivetrain_base.h
index 4dea38b..6ef519b 100644
--- a/y2017/control_loops/drivetrain/drivetrain_base.h
+++ b/y2017/control_loops/drivetrain/drivetrain_base.h
@@ -4,13 +4,9 @@
 #include "frc971/control_loops/drivetrain/drivetrain_config.h"
 
 namespace y2017 {
-namespace constants {
-// The ratio from the encoder shaft to the drivetrain wheels.
-static constexpr double kDrivetrainEncoderRatio = 1.0;
-
-}  // namespace constants
 namespace control_loops {
 namespace drivetrain {
+
 const ::frc971::control_loops::drivetrain::DrivetrainConfig &
 GetDrivetrainConfig();