Reverted: Use OS independent API for task creation/deletion

Keep existing API use in code. Bind the use of the OS independent
implementation in the systemlib layer.

Signed-off-by: Mark Charlebois <charlebm@gmail.com>

src/drivers/px4fmu/fmu.cpp

@@ -37,7 +37,7 @@
  * Driver/configurator for the PX4 FMU multi-purpose port on v1 and v2 boards.
  */
 
-#include <px4_tasks.h>
+#include <nuttx/config.h>
 
 #include <sys/types.h>
 #include <stdint.h>
@@ -302,7 +302,7 @@ PX4FMU::~PX4FMU()
 
 			/* if we have given up, kill it */
 			if (--i == 0) {
-				px4_task_delete(_task);
+				task_delete(_task);
 				break;
 			}
 
@@ -341,7 +341,7 @@ PX4FMU::init()
 	gpio_reset();
 
 	/* start the IO interface task */
-	_task = px4_task_spawn_cmd("fmuservo",
+	_task = task_spawn_cmd("fmuservo",
 			       SCHED_DEFAULT,
 			       SCHED_PRIORITY_DEFAULT,
 			       1600,