If you upload the wrong patch, or a patch with an error in it, while you are creating the review, you can remove all the files from that patch from the review, but the patch itself stays there, still attached to the review, and is listed on the review page as one of the patches that are part of the review. Unless I'm missing something, there is no way to delete the patch altogether. See the following review:

https://extranet.atlassian.com/crucible/cru/CR-FE-2296

It has 3 patches listed against it, all with the same filename, because after uploading and looking at the review I realised I had made a mistake, twice, so I reuploaded. Only one of the patches has files in it that are being included in the review. Which one is that? It doesn't say. If the functionality to delete patches were there, this wouldn't be a problem.