Constant.v: variants without Funext; cleanups #2986

Job	Run time
nix	2m 7s
quick-build (supported, ubuntu-latest)	3m 13s
build (supported)	3m 27s
quick-build (latest, ubuntu-latest)	3m 15s
build (latest)	3m 25s
opam-build (supported, ubuntu-latest)	4m 54s
quick-build (dev, ubuntu-latest)	3m 25s
opam-build (latest, ubuntu-latest)	4m 45s
build (dev, --warnings)	3m 20s
opam-build (dev, ubuntu-latest)	4m 32s
doc-dep-graphs	7m 25s
doc-alectryon	15m 4s
doc-coqdoc	1m 32s
coqchk (supported)	1m 59s
doc-timing	1m 37s
coqchk (latest)	1m 55s
install (supported)	1m 35s
coqchk (dev)	1m 47s
install (latest)	1m 35s
install (dev)	1m 45s
deploy-doc	0s
delete-artifacts	9s
	1h 12m 46s

Provide feedback