off is not a function on vm

[paulkaplan]

Submitting this so I don't forget about it. In the blocks container, there is a vm.off( in detachVM which gets triggered on componentDidMount. However, there is no such function... The correct function is (bizarrely) .removeListener :(

This never comes up right now because that component never unmounts. But playing with a tabbed area (where it actually would unmount), I saw errors coming from this.

https://github.com/LLK/scratch-gui/blob/develop/src/containers/blocks.jsx#L67-L72