All you have to do is bump into hitler's biological parents before he was conceived, and you've erased his existence. No "assassination plot" is necessary.

The butterfly effects would add up and and any zygote formed would not be the hitler-as-we-know anymore, since it would be a different combination of sperm and eggs.

Who needs guns when you got a time machine? Don't like your highschool bully, just bump into their parents back in time. Or you know, "bump" ( ͡° ͜ʖ ͡°) into their parents.