[commands] Mark CommandPtr class as [[nodiscard]] (#7803)

This has the same effect but makes it so any user code returning CommandPtr can't discard a returned command.

Signed-off-by: Eric Ward <ezeward4@gmail.com>

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

@@ -127,7 +127,6 @@ class Subsystem {
    *
    * @param action the action to run
    */
-  [[nodiscard]]
   CommandPtr RunOnce(std::function<void()> action);
 
   /**
@@ -136,7 +135,6 @@ class Subsystem {
    *
    * @param action the action to run
    */
-  [[nodiscard]]
   CommandPtr Run(std::function<void()> action);
 
   /**
@@ -146,7 +144,6 @@ class Subsystem {
    * @param start the action to run on start
    * @param end the action to run on interrupt
    */
-  [[nodiscard]]
   CommandPtr StartEnd(std::function<void()> start, std::function<void()> end);
 
   /**
@@ -156,7 +153,6 @@ class Subsystem {
    * @param run the action to run every iteration
    * @param end the action to run on interrupt
    */
-  [[nodiscard]]
   CommandPtr RunEnd(std::function<void()> run, std::function<void()> end);
 
   /**
@@ -166,7 +162,6 @@ class Subsystem {
    * @param start the action to run on start
    * @param run the action to run every iteration
    */
-  [[nodiscard]]
   CommandPtr StartRun(std::function<void()> start, std::function<void()> run);
 
   /**
@@ -176,7 +171,6 @@ class Subsystem {
    * @param supplier the command supplier.
    * @return the command.
    */
-  [[nodiscard]]
   CommandPtr Defer(wpi::unique_function<CommandPtr()> supplier);
 };
 }  // namespace frc2