ejabberdctl: Let shellcheck ignore unused ERTS_VSN

The ERTS_VSN variable is only used for releases built with Rebar 3.

ejabberdctl.template

@@ -12,6 +12,7 @@ ERLANG_NODE=ejabberd@localhost
 # define default environment variables
 [ -z "$SCRIPT" ] && SCRIPT=$0
 SCRIPT_DIR="$(cd "$(dirname "$SCRIPT")" && pwd -P)"
+# shellcheck disable=SC2034
 ERTS_VSN="{{erts_vsn}}"
 ERL="{{erl}}"
 IEX="{{bindir}}/iex"