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/channels/db/migrations/postgres/000084_recent_searches.down.sql

@@ -1 +1,2 @@
-DROP TABLE IF EXISTS recentsearches;
+-- This table is unused, and will be dropped in a future ESR.
+DROP TABLE IF EXISTS recentsearches;

server/channels/db/migrations/postgres/000084_recent_searches.up.sql

@@ -1,7 +1,8 @@
+-- This table is unused, and will be dropped in a future ESR.
 CREATE TABLE IF NOT EXISTS recentsearches (
     userid CHAR(26),
     searchpointer int,
     query jsonb,
     createat bigint NOT NULL,
     PRIMARY KEY (userid, searchpointer)
-);
+);