seqZ: rename, by, cbn -> simpl

Status Job ID Name Coverage
  Build
canceled #35531
fp
build-coq.8.10.dev

canceled #35537
fp
build-coq.8.7.2

canceled #35536
fp-timing
build-coq.8.8.0

canceled #35535
fp
build-coq.8.8.1

canceled #35534
fp
build-coq.8.8.2

canceled #35533
fp-timing
build-coq.8.9.0

canceled #35532
fp
build-coq.8.9.1

canceled #35530
fp
build-coq.dev