FreeRTOS/Arduino header include fix (#2288)

Fixes #2287

Author: earlephilhower

cores/rp2040/_freertos.h

@@ -31,12 +31,10 @@ extern bool __isFreeRTOS;
 extern volatile bool __freeRTOSinitted;
 
 extern "C" {
-#ifndef INC_FREERTOS_H
     struct QueueDefinition; /* Using old naming convention so as not to break kernel aware debuggers. */
     typedef struct QueueDefinition   * QueueHandle_t;
     typedef QueueHandle_t SemaphoreHandle_t;
     typedef int32_t BaseType_t;
-#endif
 
     extern bool __freertos_check_if_in_isr() __attribute__((weak));