Removed support for detached SCTs

[woodruffw]

Per sigstore/fulcio#1499: Fulcio may be removing detached SCT support soon, so sigstore-python can follow along.

[woodruffw]

I'm going to prioritize this, since our support for detached SCTs is now dependent on cryptography's ABCs which have been removed in 44+. See #1229.

[woodruffw]

#1236 will do this.