cbuild: drop cat /etc/apt/sources.list from debian
This file no longer exists by default on SID, so the cat fails and
stops our script. Since this command is executed via vmctl exec
, it's
not easily expanded to a condition and while more -e
works, that isn't
available on stretch.
So - since this is a basic container anyway before we make any large modifications, the sources list can usually be verified by running that same container locally. We can safely-enough drop the cat.