Circumcision is a token, sign, or seal that one was the heir of Abraham. No physical sign has the power to transfer righteousness to the doer.
Protestantism alleges that God's law is 'done away.' What Scripture shows, though, is that some aspects are not required presently, but God's law is eternal.
Parts of God's law are not presently required, yet not 'done away." Paul took a vow that required animal sacrifice. Ezekiel 34-48 shows the sacrificial law observed.
The Acts 15 decision did not do away with God's law, but solved the question of circumcision and the misconception that it was a recipe for salvation.
Jesus Christ's and Paul's example in Sabbath observance (including the annual Sabbaths) provide a model as to how we keep the Sabbath and the holy days.