rgw: remove use of s->bucket_cors

Some old code still tried to use s->bucket_cors, which was
abandoned in a cleanup work.

Signed-off-by: Yehuda Sadeh <yehuda@inktank.com>
rgw: OPTIONS request doesn't need to read object info

This is a bucket-only operation, so we shouldn't look at the
object. Object may not exist and we might respond with Not
Exists response which is not what we want.

Signed-off-by: Yehuda Sadeh <yehuda@inktank.com>