Don't set empty defaults

Empty defaults just create problems with common ansible
conventions, and is generally not a good practice.

roles/zabbix_server/defaults/main.yml

@@ -8,17 +8,17 @@ zabbix_server_manage_service: true
 # Database
 zabbix_server_database_sqlload: true
 zabbix_server_database_timescaledb: false
-zabbix_server_real_dbhost:
+#zabbix_server_real_dbhost:
 zabbix_server_dbhost: localhost
 zabbix_server_dbname: zabbix-server
 zabbix_server_privileged_host: localhost
 zabbix_server_dbencoding: utf8
 zabbix_server_dbcollation: utf8_bin
-zabbix_server_dbschema:
+#zabbix_server_dbschema:
 zabbix_server_dbuser: zabbix-server
 zabbix_server_dbpassword: zabbix-server
 zabbix_server_dbpassword_hash_method: md5
-zabbix_server_dbsocket:
+#zabbix_server_dbsocket:
 zabbix_server_dbport: 5432
 zabbix_server_dbhost_run_install: true
 zabbix_server_database: pgsql