refactor: remove [Ocaml_index.project_index] #28736

Job	Run time
Build (macos-latest, 5.1.x)	13m 22s
Build (ubuntu-latest, 5.1.x)	8m 50s
Coverage (5.1.x)	9m 32s
Coq 8.16.1	7m 18s
Build (ocaml-variants.5.3.0+trunk, ubuntu-latest, true)	4m 57s
Format	1m 1s
Build (4.14.x, ubuntu-latest, true)	1m 47s
Nix (macos-latest)	2m 8s
Build (4.14.x, macos-latest, true)	2m 56s
Build microbenchmarks	2m 18s
Create local opam switch (macos-latest, 5)	9m 15s
Nix (ubuntu-latest)	53s
Build (5.1.x, macos-13, true)	4m 18s
Create local opam switch (macos-latest, 4.14)	5m 51s
Build (ocaml-base-compiler.4.14.2,system-msvc, windows-latest)	16m 30s
Create local opam switch (ubuntu-latest, 5)	4m 44s
Build monorepo benchmark docker image	4m 27s
Build (ocaml-base-compiler.5.1.1,system-mingw, windows-latest)	10m 19s
Create local opam switch (ubuntu-latest, 4.14)	4m 59s
Build (4.08.x, ubuntu-latest, true)	1m 35s
Build (4.04.x, ubuntu-latest, true, true)	4m 40s
Documentation	50s
Build (4.02.x, ubuntu-latest, true)	4m 3s
	2h 6m 33s

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