Drop code to handle buildd images for != xenial

live-build/auto/config

@@ -630,35 +630,9 @@ case $SUBPROJECT in
 		add_package install policyrcd-script-zg2
 		add_package install pkgbinarymangler
 		add_package install ca-certificates
-		case $SUITE in
-			precise|trusty|xenial)
-				;;
-			*)
-				# only needed in >= bionic
-				add_package install gpg
-				add_package install gpg-agent
-				;;
-		esac
-		case $SUITE in
-			precise|trusty|xenial)
-				# no longer needed in >= artful
-				add_package install pkg-create-dbgsym
-				# no longer needed in >= bionic
-				add_package install apt-transport-https
-				# no longer needed in >= cosmic
-				add_package install tzdata
-				;;
-			artful)
-				# no longer needed in >= bionic
-				add_package install apt-transport-https
-				# no longer needed in >= cosmic
-				add_package install tzdata
-				;;
-			bionic)
-				# no longer needed in >= cosmic
-				add_package install tzdata
-				;;
-		esac
+		add_package install pkg-create-dbgsym
+		add_package install apt-transport-https
+		add_package install tzdata
 		add_package install fakeroot
 		add_package install build-essential
 		# Needed for LXD-based builds.