[wpilib] Remove PIDController, PIDOutput, PIDSource

Move them to the old commands vendordep so that PIDCommand and PIDSubsystem
continue to work.

This also removes Filter and LinearDigitalFilter.

wpilibc/src/main/native/cpp/AnalogPotentiometer.cpp

@@ -42,10 +42,6 @@ double AnalogPotentiometer::Get() const {
          m_offset;
 }
 
-double AnalogPotentiometer::PIDGet() {
-  return Get();
-}
-
 void AnalogPotentiometer::InitSendable(SendableBuilder& builder) {
   builder.SetSmartDashboardType("Analog Input");
   builder.AddDoubleProperty(