backups: remove noop backend

the noop backend is migrated into 0 sites config.

when the updater code sees that there is no site to backup, it will
just fail. user has to manually update with skipBackup flag.

dashboard/public/translation/zh_Hans.json

@@ -208,7 +208,6 @@
             "s3SecretAccessKey": "Secret access key",
             "gcsServiceKey": "Service Account Key",
             "format": "存储格式",
-            "noopNote": "这个选项会停用 Cloudron 的备份和恢复功能，仅应该被用于测试。请确保这台服务器已经使用其它方式备份。",
             "formatChangeNote": "使用旧存储格式的备份需要被手动删除。",
             "encryptionPassword": "加密密码（可选）",
             "advancedSettings": "高级设置…",
@@ -389,7 +388,6 @@
         "searchPlaceholder": "使用应用名称如 Github, Dropbox, Slack, Trello, ... 来搜索替代品"
     },
     "users": {
-        "newUserAction": "新用户",
         "users": {
             "user": "用户",
             "groups": "用户组",
@@ -410,7 +408,6 @@
         },
         "groups": {
             "title": "用户组",
-            "newGroupAction": "新用户组",
             "name": "名称",
             "users": "用户",
             "externalLdapTooltip": "使用外部 LDAP 目录"
@@ -893,7 +890,6 @@
     },
     "domains": {
         "title": "域名和证书",
-        "addDomain": "添加域名",
         "domain": "域名",
         "provider": "提供商",
         "tooltipEdit": "编辑域名",
@@ -1589,7 +1585,6 @@
             "addAction": "添加",
             "title": "添加磁盘卷"
         },
-        "addVolumeAction": "添加卷",
         "name": "名称",
         "hostPath": "主机路径",
         "removeVolumeDialog": {