Remove command palette POC (#24044)

* Revert "POC: Cross-team recent search (#20027)"

This reverts commit aa59c28b04, preserving
a few code tidyings unrelated to the original PR.

* Revert "Add feature flag for command palette (#20011)"

This reverts commit c78c5ce3f3.

server/i18n/en.json

@@ -6403,10 +6403,6 @@
     "id": "app.reaction.save.save.app_error",
     "translation": "Unable to save reaction."
   },
-  {
-    "id": "app.recent_searches.app_error",
-    "translation": "Error fetching recent searches"
-  },
   {
     "id": "app.recover.delete.app_error",
     "translation": "Unable to delete token."