doc: remove dune:stanza directive #25779

Job	Run time
MSVC 4.14.0 / windows_x86	12m 1s
MSVC 4.14.0 / windows_x86_64	11m 33s
Coverage (4.14.x)	11m 58s
Build (macos-latest, 4.14.x)	28m 57s
Documentation	34s
Build (ubuntu-latest, 4.14.x)	11m 28s
Build (windows-latest, 4.14.x)	6m 46s
Format	2m 23s
Nix (macos-latest)	3m 13s
Build (ocaml-variants.5.2.0+trunk, ubuntu-latest, true)	2m 26s
Nix (ubuntu-latest)	57s
Build (5.1.x, ubuntu-latest, true)	2m 19s
Build (5.1.x, macos-latest, true)	4m 48s
Build (4.13.x, ubuntu-latest, true)	2m 23s
Coq 8.16.1	8m 51s
Build (4.08.x, ubuntu-latest, true)	2m 18s
Build (4.04.x, ubuntu-latest, true, true)	5m 54s
Create local opam switch (macos-latest, 5)	17m 15s
Build (4.02.x, ubuntu-latest, true)	4m 44s
Create local opam switch (macos-latest, 4.14)	11m 37s
Create local opam switch (ubuntu-latest, 5)	5m 2s
Create local opam switch (ubuntu-latest, 4.14)	5m 7s
Build monorepo benchmark docker image	1m 54s
	2h 44m 28s

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