Specifically install libexpat1-dev

This stops:
  debug: Puppet::Type::Package::ProviderApt: Executing '/usr/bin/apt-get -q -y -o DPkg::Options::=--force-confold install git-completion'
  notice: /Stage[main]/Libexpat-dev/Package[libexpat-dev]/ensure: ensure changed 'purged' to 'latest'
Don't install git-completion package

It's part of git on Ubuntu. If we need it elsewhere, we'll deal with it then.