Undo Oxford snapshot

Undoes the initial Oxford snapshot (!9140 (merged)).

Steps taken to produce this MR

1. Purge src/protocol_018*
2. Remove the Oxford-related packages from the manifest, devtools, etc
3. Remove Oxford from tests
4. Remove Oxford from documentation
5. Incorporate previously deleted Oxford changelog items back into the latest Alpha changelog

Notes

I left the Oxford-related changes in src/lib_scoru_wasm, they don't cause any friction in this state and would otherwise be reintroduced in the exact same way later.