remove the in-kernel struct dirent{,64}

The kernel struct dirent{,64} were different from the ones in
userspace.

Even worse, we exported the kernel ones to userspace.

But after the fat usages are fixed we can remove the conflicting
kernel versions.

Reviewed-by: H. Peter Anvin <hpa@kernel.org>
Signed-off-by: Adrian Bunk <bunk@kernel.org>
Cc: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>