Fix proofs in Script_timestamp.v
Port the file https://nomadic-labs.gitlab.io/coq-tezos-of-ocaml/docs/proto_alpha/proofs/script_timestamp/ to Proto K.
Port the file https://nomadic-labs.gitlab.io/coq-tezos-of-ocaml/docs/proto_alpha/proofs/script_timestamp/ to Proto K.