lsm: remove obsoleted comments for security hooks

Remove the following obsoleted comments for security hooks:

1. sb_copy_data, the hook function has been removed since
commit 5b400239 ("LSM: turn sb_eat_lsm_opts() into a method").

2. sb_parse_opts_str, the hook function has been removed since
commit 757cbe59 ("LSM: new method: ->sb_add_mnt_opt()").

They are obsoleted comments, so remove them.

Signed-off-by: Gaosheng Cui <cuigaosheng1@huawei.com>
Reviewed-by: Casey Schaufler <casey@schaufler-ca.com>
[PM: subj line tweaks]
Signed-off-by: Paul Moore <paul@paul-moore.com>