remove dlib and armlibc sys folder

components/libc/compilers/armlibc/sys/README.md

-Because Keil MDK leaks some system header file, we put them in here. 
\ No newline at end of file

components/libc/compilers/armlibc/sys/errno.h

-/*
- * Copyright (c) 2006-2021, RT-Thread Development Team
- *
- * SPDX-License-Identifier: Apache-2.0
- *
- * Change Logs:
- * Date           Author       Notes
- */
-#ifndef SYS_ERRNO_H__
-#define SYS_ERRNO_H__
-
-#include <rtthread.h>
-
-#endif

components/libc/compilers/common_except_gcc/readme.md

+## Attentions
+
+This folder is "common" for armlibc and dlib.
\ No newline at end of file

components/libc/compilers/dlib/sys/README.md

-Because IAR leaks some system header file, we put them in here. 
\ No newline at end of file

components/libc/compilers/dlib/sys/errno.h

-/*
- * Copyright (c) 2006-2021, RT-Thread Development Team
- *
- * SPDX-License-Identifier: Apache-2.0
- *
- * Change Logs:
- * Date           Author       Notes
- * 2019-07-08     Bernard      The first version
- */
-
-#ifndef SYS_ERRNO_H__
-#define SYS_ERRNO_H__
-
-#include <errno.h>
-
-#endif

components/libc/compilers/dlib/sys/signal.h

-/*
- * Copyright (c) 2006-2021, RT-Thread Development Team
- *
- * SPDX-License-Identifier: Apache-2.0
- *
- * Change Logs:
- * Date           Author       Notes
- * 2019-07-08     Bernard      The first version
- */
-
-#ifndef SYS_SIGNAL_H__
-#define SYS_SIGNAL_H__
-
-#include <libc/libc_signal.h>
-
-#endif