remove extra wharfie

The problem here is the single quotes which cause the $(pwd) to not be expanded. This should be: 

boot2docker ssh "sudo modprobe vboxsf && sudo mkdir -p $(pwd)/trees/ && sudo mount -t vboxsf trees $(pwd)/trees"

I'll fix the docs for now and make a bug for a command to do this so we don't need to rely on running commands that need to be run from a specific dir.

Also the hosts file command has the same issue with single quotes.