fix: rename duplicate migration (#8989)

coderd/database/migrations/000149_agent_multiple_subsystems.down.sql

@@ -0,0 +1,17 @@
+BEGIN;
+
+-- Bring back the subsystem column.
+ALTER TABLE workspace_agents ADD COLUMN subsystem workspace_agent_subsystem NOT NULL DEFAULT 'none';
+
+-- Update all existing workspace_agents to have subsystem = subsystems[0] unless
+-- subsystems is empty.
+UPDATE workspace_agents SET subsystem = subsystems[1] WHERE cardinality(subsystems) > 0;
+
+-- Drop the subsystems column from workspace_agents.
+ALTER TABLE workspace_agents DROP COLUMN subsystems;
+
+-- We cannot drop the "exectrace" value from the workspace_agent_subsystem type
+-- because you cannot drop values from an enum type.
+UPDATE workspace_agents SET subsystem = 'none' WHERE subsystem = 'exectrace';
+
+COMMIT;