Fix DCE/Subst01 to work under lambdas (#1809) #358

Job	Run time
docker-master	1h 41m 40s
publish-standalone-dry-run	20s
test-standalone (master, dev, default)	49s
build-wasm-of-ocaml (master, 4.14.1)	12m 48s
build-js-of-ocaml (master, 4.11.1)	17m 27s
generated-files (master)	40s
standalone-haskell (master)	52m 8s
test-amd64	2h 18m 13s
validate-docker-master	32m 28s
deploy-js-wasm-of-ocaml	2m 13s
docker-check-all	2s
	5h 58m 48s

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