Maybe so, I'd be really curious to talk to a UK lawyer who has some experience in these matters to get a sense for how they're enforced. Thanks for asking the question and inspiring me to do the research - like you I assumed there was no way "delete" was regulated, but decided to look it up before replying and was very surprised.
I think you could easily argue that "needing it for an undo feature" is still a legal use for that data. But, thanks for pointing out that "delete" is a lot more legally loaded a term than I had assumed. It makes a pretty convincing case to call things "remove" instead of "delete".