fix: remove duplicate IncidentNotificationMatrix type export causing TS2300 error

Co-authored-by: hotlong <50353452+hotlong@users.noreply.github.com>

Author: Copilot

packages/spec/src/system/incident-response.zod.ts

@@ -365,4 +365,3 @@ export type IncidentCategory = z.infer<typeof IncidentCategorySchema>;
 export type IncidentStatus = z.infer<typeof IncidentStatusSchema>;
 export type Incident = z.infer<typeof IncidentSchema>;
 export type IncidentResponsePolicy = z.infer<typeof IncidentResponsePolicySchema>;
-export type IncidentNotificationMatrix = z.infer<typeof IncidentNotificationMatrixSchema>;