Removes ruby dependencies from Debian/Ubuntu preseed templates

This pull request does for the Ubuntu and Debian preseed templates what @jcpowermac's recent PR (#305) did for the RHEL/CentOS kickstart templates. With these changes in place, no model should install ruby as part of the minimal install (although it may be installed later as part of Puppet and/or Chef broker handoff process using the preferred method for installing Ruby during the install and configuration of the selected broker, if any).