Revert "[FedCM] Enable CORS in ID assertion endpoint"

This reverts commit b2cb1b55ae3c4f7b88a74a0ceb697646fde03a5b.

Reason for revert: Causing issues to a real IDP

Original change's description:

[FedCM] Enable CORS in ID assertion endpoint

I2S: https://groups.google.com/a/chromium.org/g/blink-dev/c/gYoQJsaiD9E

Bug: 40284123 Change-Id: I61989f1e7a7578c2f59d87815e3ec2b51b7fc5be Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5370086 Reviewed-by: Nasko Oskov nasko@chromium.org Reviewed-by: Christian Dullweber dullweber@chromium.org Reviewed-by: Mathias Bynens mathias@chromium.org Commit-Queue: Nicolás Peña npm@chromium.org Cr-Commit-Position: refs/heads/main@{#1274203}

Bug: 40284123 Change-Id: I4a518b55396d5aba676f0a15c9a515451dc11e86 Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5381316 Reviewed-by: Christian Biesinger cbiesinger@chromium.org Reviewed-by: Mathias Bynens mathias@chromium.org Commit-Queue: Nicolás Peña npm@chromium.org Reviewed-by: Nasko Oskov nasko@chromium.org Reviewed-by: Christian Dullweber dullweber@chromium.org Bot-Commit: Rubber Stamper rubber-stamper@appspot.gserviceaccount.com Cr-Commit-Position: refs/heads/main@{#1276213}