ext4: Remove (partial, never completed) fragment support

Fragment support in ext2/3/4 was never implemented, and it probably will
never be implemented.   So remove it from ext4.

Signed-off-by: Coly Li <coyli@suse.de>
Acked-by: Andreas Dilger <adilger@clusterfs.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>