Revert "apt: Move sources into sources.list to make other packages happy"

This reverts commit df3e541400f3bd1340403631e68d44f8e41478ba. This change had
knock-on effects that caused apt to misbehave w.r.t. the mdt-services local apt
repo.

Change-Id: I24266d6f4b5abe0b7c51033b158bd9ed6480963a
diff --git a/etc/runonce.d/99-cleanup-sources b/etc/runonce.d/99-cleanup-sources
deleted file mode 100755
index 27c7ca9..0000000
--- a/etc/runonce.d/99-cleanup-sources
+++ /dev/null
@@ -1,5 +0,0 @@
-#!/bin/bash
-
-cat /etc/apt/sources.list.d/multistrap-*.list >>/etc/apt/sources.list
-rm -f /etc/apt/sources.list.d/multistrap-*.list
-