audit: remove selinux_audit_rule_update() declaration

selinux_audit_rule_update() has been renamed to audit_update_lsm_rules()
since commit d7a96f3a ("Audit: internally use the new LSM audit
hooks"), so remove it.

Signed-off-by: Xiu Jianfeng <xiujianfeng@huawei.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>