contrib/actions: drop custom sources.list

(cherry picked from commit 394bc8e6)

contrib/actions/install-dependencies.sh

@@ -2,8 +2,6 @@
 
 set -e
 
-cp contrib/actions/sources.list /etc/apt/sources.list
-rm -rf /etc/apt/sources.list.d
 apt-get update
 apt-get install git subversion build-essential python gawk unzip libncurses-dev zlib1g-dev libssl-dev wget time
 apt-get clean

contrib/actions/sources.list

-deb http://mirror.netcologne.de/ubuntu/ bionic main restricted
-deb http://mirror.netcologne.de/ubuntu/ bionic-updates main restricted