ext2: Drop fragment support

commit 404615d7 upstream.

Ext2 has fields in superblock reserved for subblock allocation support.
However that never landed. Drop the many years dead code.

Reported-by:  <syzbot+af5e10f73dbff48f70af@syzkaller.appspotmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>