You can never get rid of your darkside, you can reject it, fight it, but never get rid of it. Its a constant battle and that’s the point. Taking the path of the light is vowing to fight this battle.
To be fair Yoda conquered his dark side in The Clone Wars and yet he never struggled with it ever again
Pressuring Luke to kill his father isn’t very lightside ; )
Well… at least Yoda wasn’t intending to kill Vader by himself.