Remove SampleRobot (#1658)

SampleRobot provides no benefits over RobotBase to advanced teams and
TimedRobot is recommended for everyone else.

A skeleton template for RobotBase was added.

wpilibcExamples/src/main/cpp/templates/robotbaseskeleton/include/Robot.h

@@ -0,0 +1,21 @@
+/*----------------------------------------------------------------------------*/
+/* Copyright (c) 2018-2019 FIRST. All Rights Reserved.                        */
+/* Open Source Software - may be modified and shared by FRC teams. The code   */
+/* must be accompanied by the FIRST BSD license file in the root directory of */
+/* the project.                                                               */
+/*----------------------------------------------------------------------------*/
+
+#pragma once
+
+#include <frc/RobotBase.h>
+
+class Robot : public frc::RobotBase {
+ public:
+  void RobotInit();
+  void Disabled();
+  void Autonomous();
+  void Teleop();
+  void Test();
+
+  void StartCompetition() override;
+};