You can remove the attachment by going to "Edit Post" and at the bottom you will have then an option to "Go Advanced". If you do that then you will see below the message a section called "Attachments" and that is where you can delete the attachment. I can do it for you if you wish so or, if you want to do it yourself, please go ahead.
Can't comment on the bracket, but if you were worried about losing it, a simple safety line from the gopro to ,say, the helmet buckle, should do the trick. That way, worst case scenario will see it fly lose and start wacking you on the shoulder. I'd use appropriately rated nylon fishing line, or cord. Keep it short so it can't whip around your neck and choke/cut you!