Too many people writing a letter of recommendation
It's ruder to waste their time. Just send a simple email saying "Thank you for agreeing to write a letter for me, however I realised I accidentally asked too many people to write letters for me for this position, so you don't need to continue writing one for me. I would still like to ask you to write a letter for me in the future, if I decide to apply to other opportunities. Is that ok with you?".

Either they will agree, in which case great, or they'll say no, and eventually you will have to find someone else. My advice would be to ask your letter writers a long way in advance of the deadline, to avoid you having to rush around asking multiple people at the last minute. You will likely get a stronger letter that way too.