The system where we got a replacement day for working on Saturdays is over.
「土曜出勤」= "Work on Saturday"
「振替」= "transfer", "exchange"
「代休」= "compensatory holiday", "replacement day"
「制度」= "system"
「なくなる」= "to disappear", "to go away", "to end"など
例文:
「土曜出勤の振替代休の制度がなくなりました。」
"The system where we got a replacement day for working on Saturdays is over."
「祝日出勤すれば代休をもらいます。」
"If you work on holidays, you'll get replacement days."
ご参考になれば幸いです。