ext4: get rid of some obsolete EXT4_MB_HINT flags

Since nobody has used these EXT4_MB_HINT flags for ages,
let's remove them.

Signed-off-by: Baokun Li <libaokun1@huawei.com>
Reviewed-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Zhang Yi <yi.zhang@huawei.com>
Link: https://patch.msgid.link/20250714130327.1830534-7-libaokun1@huawei.com


Signed-off-by: Theodore Ts'o <tytso@mit.edu>