Start using the new FRC compiler define (#797)

Remove all definitions from the MockData headers when in simulation mode.
Add a constexpr IsReal and IsSimulation in RobotBase.

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

@@ -52,6 +52,16 @@ class RobotBase {
   static std::thread::id GetThreadId();
   virtual void StartCompetition() = 0;
 
+  static constexpr bool IsReal() {
+#ifdef __FRC_ROBORIO__
+    return true;
+#else
+    return false;
+#endif
+  }
+
+  static constexpr bool IsSimulation() { return !IsReal(); }
+
  protected:
   RobotBase();
   virtual ~RobotBase() = default;