[commands] Remove deprecated C++ method TransferOwnership (#6780)

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

@@ -487,13 +487,6 @@ class Command : public wpi::Sendable, public wpi::SendableHelper<Command> {
   /// Requirements set.
   wpi::SmallSet<Subsystem*, 4> m_requirements;
 
-  /**
-   * Transfers ownership of this command to a unique pointer.  Used for
-   * decorator methods.
-   */
-  [[deprecated("Use ToPtr() instead")]]
-  virtual std::unique_ptr<Command> TransferOwnership() && = 0;
-
   std::optional<std::string> m_previousComposition;
 };