[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/ParallelDeadlineGroup.h

@@ -17,7 +17,7 @@
 
 #include <wpi/DecayedDerivedFrom.h>
 
-#include "frc2/command/CommandGroupBase.h"
+#include "frc2/command/CommandBase.h"
 #include "frc2/command/CommandHelper.h"
 
 namespace frc2 {
@@ -34,7 +34,7 @@ namespace frc2 {
  * This class is provided by the NewCommands VendorDep
  */
 class ParallelDeadlineGroup
-    : public CommandHelper<CommandGroupBase, ParallelDeadlineGroup> {
+    : public CommandHelper<CommandBase, ParallelDeadlineGroup> {
  public:
   /**
    * Creates a new ParallelDeadlineGroup. The given commands (including the
@@ -73,6 +73,11 @@ class ParallelDeadlineGroup
   // Prevent template expansion from emulating copy ctor
   ParallelDeadlineGroup(ParallelDeadlineGroup&) = delete;
 
+  /**
+   * Adds the given commands to the group.
+   *
+   * @param commands Commands to add to the group.
+   */
   template <wpi::DecayedDerivedFrom<Command>... Commands>
   void AddCommands(Commands&&... commands) {
     std::vector<std::unique_ptr<Command>> foo;
@@ -97,7 +102,7 @@ class ParallelDeadlineGroup
   void InitSendable(wpi::SendableBuilder& builder) override;
 
  private:
-  void AddCommands(std::vector<std::unique_ptr<Command>>&& commands) final;
+  void AddCommands(std::vector<std::unique_ptr<Command>>&& commands);
 
   void SetDeadline(std::unique_ptr<Command>&& deadline);