scripts: Remove obsolete zesty configuration.

Zesty already reached end-of-life, so we'll never support it.

And in one place, we add support for bionic.

scripts/lib/setup-apt-repo

@@ -10,7 +10,7 @@ apt-get install -y lsb-release apt-transport-https
 SCRIPTS_PATH="$(dirname $(dirname $0))"
 
 release=$(lsb_release -sc)
-if [ "$release" = "trusty" ] || [ "$release" = "xenial" ] || [ "$release" = "zesty" ]; then
+if [ "$release" = "trusty" ] || [ "$release" = "xenial" ] || [ "$release" = "bionic" ]; then
     apt-key add "$SCRIPTS_PATH"/setup/pgroonga-ppa.asc
     apt-key add "$SCRIPTS_PATH"/setup/zulip-ppa.asc
     cat >/etc/apt/sources.list.d/zulip.list <<EOF

tools/lib/provision.py

@@ -110,7 +110,6 @@ POSTGRES_VERSION_MAP = {
     "stretch": "9.6",
     "trusty": "9.3",
     "xenial": "9.5",
-    "zesty": "9.6",
     "bionic": "10",
 }
 POSTGRES_VERSION = POSTGRES_VERSION_MAP[codename]