docs(rum): hide Flutter SDK nav until console ships

Flutter docs landed on main ahead of the console production release.
Drop the zh/en sidebar groups so the pages stay out of navigation until
fc-saas-rum #255 reaches production; page files are kept for a one-line restore.

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: Fiona2016

docs.json

@@ -419,15 +419,6 @@
                       "zh/rum/sdk/harmony/data-collection"
                     ]
                   },
-                  {
-                    "group": "Flutter",
-                    "pages": [
-                      "zh/rum/sdk/flutter/sdk-integration",
-                      "zh/rum/sdk/flutter/advanced-config",
-                      "zh/rum/sdk/flutter/compatible",
-                      "zh/rum/sdk/flutter/data-collection"
-                    ]
-                  },
                   {
                     "group": "微信小程序",
                     "pages": [
@@ -1657,15 +1648,6 @@
                       "en/rum/sdk/harmony/data-collection"
                     ]
                   },
-                  {
-                    "group": "Flutter",
-                    "pages": [
-                      "en/rum/sdk/flutter/sdk-integration",
-                      "en/rum/sdk/flutter/advanced-config",
-                      "en/rum/sdk/flutter/compatible",
-                      "en/rum/sdk/flutter/data-collection"
-                    ]
-                  },
                   {
                     "group": "WeChat Mini Program",
                     "pages": [