ext4: remove duplicate include of ext4_fs_i.h header file

include/linux/ext4_fs_i.h is included in include/linux/ext_fs.h twice
Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Mingming Cao <cmm@us.ibm.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>