[commands] Deprecate C++ TransferOwnership() (#6095)

It has been completely replaced with ToPtr().

wpilibNewCommands/src/main/native/include/frc2/command/CommandHelper.h

@@ -8,6 +8,8 @@
 #include <memory>
 #include <utility>
 
+#include <wpi/deprecated.h>
+
 #include "frc2/command/Command.h"
 #include "frc2/command/CommandPtr.h"
 
@@ -34,6 +36,7 @@ class CommandHelper : public Base {
   }
 
  protected:
+  WPI_DEPRECATED("Use ToPtr() instead")
   std::unique_ptr<Command> TransferOwnership() && override {
     return std::make_unique<CRTP>(std::move(*static_cast<CRTP*>(this)));
   }