It isn't censorship. No one is telling Parler they're not free to do what they want. AWS is telling Parler they don't want them as a customer. That is not censorship. Whether a business should be able to refuse a customer is an interesting question. People on the political right have historically believed they should (refusing to make a wedding cake for a gay couple is often cited as a case of such freedom).
There is also an argument that AWS is now so big and important that they should be treated like a utility, and then refusing customers is something that they shouldn't necessarily be allowed to do. I'm not sure how I feel about that argument though.
There is also an argument that AWS is now so big and important that they should be treated like a utility, and then refusing customers is something that they shouldn't necessarily be allowed to do. I'm not sure how I feel about that argument though.