fix: remove migration 019, table was dropped manually

migrations/019_fix_chat_histories_fk.sql

@@ -1,11 +0,0 @@
--- Migration: 019_fix_chat_histories_fk
--- Fix the project_id foreign key on chat_histories to reference projects(guid)
--- instead of projects(id). This corrects the initial migration (018) which
--- used the wrong column — projects.id is a bigserial, projects.guid is the UUID.
-
-ALTER TABLE chat_histories
-    DROP CONSTRAINT IF EXISTS chat_histories_project_id_fkey;
-
-ALTER TABLE chat_histories
-    ADD CONSTRAINT chat_histories_project_id_fkey
-    FOREIGN KEY (project_id) REFERENCES projects(guid) ON DELETE SET NULL;