chmod.2, chown.2, open.2, mkdir.2, mknod.2, readlink.2, stat.2, symlink.2, mkfifo...

chmod.2, chown.2, open.2, mkdir.2, mknod.2, readlink.2, stat.2, symlink.2, mkfifo.3, scandir.3, sem_wait.3: ERRORS: combine errors into a single alphabetic list

These pages split out extra errors for some APIs into a separate
list.  Probably, the pages are easier to ready if all errors are
combined into a single list.

Note that there still remain a few pages where the errors are
listed separately for different APIs. For the moment, it seems
best to leave those pages as is, since the error lists are
largely distinct in those pages.

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>