[commands] Remove deprecated classes and functions (#5409)

Removes:
- PerpetualCommand
- Command.perpetually()
- CommandGroupBase
- Command.IsGrouped() (C++ only)
- Command.SetGrouped() (C++ only)
- Command.withInterrupt()
- ProxyScheduleCommand
- Button
- InternalButton, JoystickButton, NetworkButton and POVButton now subclass Trigger
- Old style Trigger functions:
    - Trigger.whenActive
    - Trigger.whileActiveOnce
    - Trigger.whileActiveContinuous
    - Trigger.whenInactive
    - Trigger.toggleWhenActive
    - Trigger.cancelWhenActive
- CommandScheduler.clearButtons()
- CommandScheduler.addButtons() (Java only)
- Command supplier constructor of SelectCommand

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

@@ -77,12 +77,6 @@ class CommandScheduler final : public nt::NTSendable,
    */
   frc::EventLoop* GetDefaultButtonLoop() const;
 
-  /**
-   * Removes all button bindings from the scheduler.
-   */
-  [[deprecated("Call Clear on the EventLoop instance directly!")]]
-  void ClearButtons();
-
   /**
    * Schedules a command for execution. Does nothing if the command is already
    * scheduled. If a command's requirements are not available, it will only be