Our Zuul executors already have the openafs-client role which
includes a /etc/apt/sources.list.d/openafs.list file for our PPA
with custom OpenAFS package backports. The zuul-executor role
doesn't need to add another copy (and the duplicate is breaking apt
now).
Change-Id: Icdb6d2f3bf36b0cad901d42c3d97873677ee87cb
1ce56c7ce2