Don't define forwarded ports in the box

Due to the Vagrantfile merging algorithm, having default port forwarding in the box breaks multi-VM port forwarding setups.

http://docs.vagrantup.com/v2/vagrantfile/index.html

See WinRb/vagrant-windows#171 for more info.

My host also has WinRM activated, so this standard port forwarding setup always halts vagrant up.