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/cpp/IterativeRobotBase.cpp

@@ -146,13 +146,6 @@ void IterativeRobotBase::TestPeriodic() {
   }
 }
 
-IterativeRobotBase::IterativeRobotBase() {
-  RobotInit();
-
-  // Tell the DS that the robot is ready to be enabled
-  HAL_ObserveUserProgramStarting();
-}
-
 void IterativeRobotBase::LoopFunc() {
   // Call the appropriate function depending upon the current robot mode
   if (IsDisabled()) {