SetoidRewrite: various cleanups and simplifications #3889

Job	Run time
quick-build (latest, ubuntu-latest)	3m 31s
opam-build (supported, ubuntu-latest)	5m 7s
opam-build (latest, ubuntu-latest)	4m 41s
quick-build (dev, ubuntu-latest)	3m 18s
quick-build (supported, ubuntu-latest)	3m 36s
opam-build (dev, ubuntu-latest)	4m 15s
nix	2m 12s
build (latest)	3m 57s
build (dev, --warnings)	3m 21s
build (supported)	3m 45s
doc-dep-graphs	1m 14s
doc-alectryon	1m 14s
doc-timing	1m 13s
doc-coqdoc	1m 13s
coqchk (latest)	1m 7s
install (latest)	1m 12s
coqchk (supported)	1m 13s
install (dev)	1m 14s
install (supported)	1m 13s
coqchk (dev)	1m 14s
deploy-doc	1s
delete-artifacts	6s
	49m 57s

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