Erasing your Reddit history is an asshole move, and does not really help "the cause"
Users removing their entire Reddit history might block people from reaching useful info that was in that history. Think of people, who may not be Redditors themselves, searching in the future via google, or whatever, for some useful info that was in your deleted history, just because you wanted
to feel good about yourself sticking it to spez, or just because you blindly followed the manic sheeple who advised you to do so.
Deleting your entire Reddit history does not help the cause, not proactively anyway.
What would help the cause is people knowing that a very useful/knowledgeable/interesting user, as evidenced by their Reddit history, has abandoned their platform. Even better, if people knew that the useful/knowledgeable/interesting user has moved to a new platform called Lemmy.
Whether you are planning to leave Reddit completely, or you are splitting your time between here and there, leaving a message like the one below at the end of comments, and/or in its own stickied post in your profile, would be much more helpful than trying to erase your Reddit history: