ext3/ext4 Documentation: remove bh/nobh since it has been deprecated

Bh and nobh mount option has been deprecated in ext4
(206f7ab4) and in ext3
(4c4d3901)
so remove those options from documentation.

Signed-off-by: Lukas Czerner <lczerner@redhat.com>
Reviewed-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Jan Kara <jack@suse.cz>