roles/common: Remove task which removes irqbalance

Prevailing wisdom is actually that this *can* help virtual hosts,
especially when the VM guest has multiple CPUs.

See: http://wiki.xen.org/wiki/Network_Throughput_and_Performance_Guide

Signed-off-by: Alan Orth <alan.orth@gmail.com>
vars/Debian.yml: Update apt mirror to Linode one

Signed-off-by: Alan Orth <alan.orth@gmail.com>