CONFIG_EXT3_INDEX is not an exposed config option in the kernel, and it is
unconditionally defined in ext3_fs.h.  tune2fs is already able to turn off
dir indexing, so at this point it's just cluttering up the code.  Remove
it.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Cc: <linux-ext4@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>