Clean up drive class implementations

Left and right sides of the differential drive and mecanum drive classes
are now both forward and the "inversion multiplier" was removed.

The deadband functionality was moved to GenericHID::GetRawAxis() since
the deadband is generally applied to joystick axes.

MotorSafety was removed since that's handled by the drivetrain's motor
controllers already.

RobotDrive was removed because it's been deprecated for several years
and was only used in tests.

wpilibc/src/main/native/cpp/GenericHID.cpp

@@ -4,6 +4,8 @@
 
 #include "frc/GenericHID.h"
 
+#include <cmath>
+
 #include <hal/DriverStation.h>
 
 #include "frc/DriverStation.h"
@@ -31,7 +33,7 @@ bool GenericHID::GetRawButtonReleased(int button) {
 }
 
 double GenericHID::GetRawAxis(int axis) const {
-  return m_ds->GetStickAxis(m_port, axis);
+  return ApplyDeadband(m_ds->GetStickAxis(m_port, axis), m_deadband);
 }
 
 int GenericHID::GetPOV(int pov) const {
@@ -95,3 +97,17 @@ void GenericHID::SetRumble(RumbleType type, double value) {
   }
   HAL_SetJoystickOutputs(m_port, m_outputs, m_leftRumble, m_rightRumble);
 }
+
+void GenericHID::SetAxisDeadband(double deadband) { m_deadband = deadband; }
+
+double GenericHID::ApplyDeadband(double value, double deadband) {
+  if (std::abs(value) > deadband) {
+    if (value > 0.0) {
+      return (value - deadband) / (1.0 - deadband);
+    } else {
+      return (value + deadband) / (1.0 - deadband);
+    }
+  } else {
+    return 0.0;
+  }
+}