osal clean up

remove OSAL_TASK_DEF, osal_task_create. Applicaton should create a task
and call tinyusb_task(). This make API consistent with NO OS.

src/tusb.h

@@ -105,11 +105,9 @@
 // return true if success
 bool tusb_init(void);
 
-#if CFG_TUSB_OS == OPT_OS_NONE
-/** \brief Run all tinyusb's internal tasks (e.g host task, device task).
- * \note   This function is only required when using no RTOS (\ref CFG_TUSB_OS == OPT_OS_NONE). All the stack functions
- *         & callback are invoked within this function. This should be called periodically within the mainloop
- *
+/** Run all tinyusb's internal tasks (e.g host task, device task) and invoke callback
+ * This should be called periodically within the mainloop.
+
     @code
     int main(void)
     {
@@ -126,10 +124,9 @@ bool tusb_init(void);
       }
     }
     @endcode
- *
+
  */
 void tusb_task(void);
-#endif
 
 /** @} */