Fix IterativeRobot/TimedRobot RobotInit(). (#633)

In C++, it's not legal to call a virtual function from within a constructor,
so the user override was never called (the base function is always called).

See https://isocpp.org/wiki/faq/strange-inheritance#calling-virtuals-from-ctors

While this is technically allowed in Java, also change Java for consistency.

wpilibc/src/main/native/include/IterativeRobotBase.h

@@ -55,7 +55,6 @@ class IterativeRobotBase : public RobotBase {
   virtual void TestPeriodic();
 
  protected:
-  IterativeRobotBase();
   virtual ~IterativeRobotBase() = default;
 
   void LoopFunc();