deployments-calendar: Remove standing Technical Engagement window

bd808 will be out on sabbatical 2023-09-01 through 2023-10-31. There is currently no active backfill for him during that period, so we can reduce IRC noise and possible confusion about the standing Thursday window by leaving it out of schedules while he is gone. We can re-evaluate in November 2023 if the window should return and what it should be named now that Technical Engagement has been disbanded.