Update listen_ssl.template deprecated http2 on listener

data/conf/nginx/templates/listen_ssl.template

@@ -1,2 +1,3 @@
-listen ${HTTPS_PORT} ssl http2;
-listen [::]:${HTTPS_PORT} ssl http2;
+listen ${HTTPS_PORT} ssl;
+listen [::]:${HTTPS_PORT} ssl;
+http2 on;