munmap/munmap03.c: cleanup

Delete the useless code doing mmap operation on a file, which
makes no sense in this case.

Use safe macros and do some code re-arrangement.

Some cleanup.

Signed-off-by: Xiaoguang Wang <wangxg.fnst@cn.fujitsu.com>
munmap/munmap03.c: make EINVAL error value tests sufficient

Signed-off-by: Xiaoguang Wang <wangxg.fnst@cn.fujitsu.com>