Removes a directory file.
    Format
      #include  <unistd.h>
      int rmdir  (const char *path);
1 – Argument
 path
    A directory pathname.
2 – Description
    The rmdir function removes a directory file whose name is
    specified in the path argument. The directory is removed only
    if it is empty.
    If path names a symbolic link, then rmdir fails and sets errno to
    ENOTDIR.
3 – Restriction
    When using OpenVMS format names, the path argument must be in the
    form directory.dir.
4 – Return Values
    0                  Indicates success.
    -1                 An error occurred; errno is set to indicate
                       the error.