removed unused etc files

core/Dockerfile

@@ -4,7 +4,7 @@ RUN <<EOF
 export DEBIAN_FRONTEND=noninteractive 
 export TZ=Europe/Berlin 
 apt-get update
-apt-get install -y --no-install-recommends tzdata wget gnupg ca-certificates
+apt-get install -y --no-install-recommends tzdata wget gnupg ca-certificates bind9-dnsutils
 update-ca-certificates
 # install core
 wget --no-verbose -P/tmp http://bldr/core-11.0.2.50.507cbae-Ubuntu_20.04-amd64.tar.gz