Remove __annonCompField offsets from witness invariants #14473

Job	Run time
regression (ubuntu-22.04, ocaml-variants.4.14.2+options,ocaml-option-flambda)	8m 25s
regression (macos-13, ocaml-variants.4.14.2+options,ocaml-option-flambda)	24m 38s
extraction	0s
	33m 3s

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