Revert "client-admin partly converted to react router v6 (#51)" (#148)

This reverts commit a385f66.

Author: thomassth

client-admin/package-lock.json

@@ -62,7 +62,7 @@
     "react-dom": "^18.3.1",
     "react-easy-emoji": "~1.8.1",
     "react-redux": "^9.1.2",
-    "react-router-dom": "^6.27.0",
+    "react-router-dom": "^5.3.4",
     "redux": "^5.0.0",
     "redux-thunk": "~2.3.0",
     "theme-ui": "^0.16.2",