Removing multiple forwarded port declaration

This fixes:

    ➜  rethinkdb-vagrant git:(master) ✗ ./rethinkdb.sh                                                
    There were warnings and/or errors while loading your Vagrantfile
    for the machine 'default'.
    
    Your Vagrantfile was written for an earlier version of Vagrant,
    and while Vagrant does the best it can to remain backwards
    compatible, there are some cases where things have changed
    significantly enough to warrant a message. These messages are
    shown below.

    Warnings:
    * `config.vm.customize` calls are VirtualBox-specific. If you're
    using any other provider, you'll have to use config.vm.provider in a
    v2 configuration block.

    Bringing machine 'default' up with 'virtualbox' provider...
    There are errors in the configuration of this machine. Please fix
    the following errors and try again:

    vm:
    * Forwarded port '2222' (host port) is declared multiple times
    with the protocol 'tcp'.