Remove some unused syntax error cases #6658

Job	Run time
build-compiler (ubuntu-24.04, ocaml-variants.5.3.0+options,ocaml-option-static, true, true, linux...	16m 46s
build-rewatch (macos-13, x86_64-apple-darwin, darwin-x64)	2m 5s
build-compiler (ubuntu-24.04-arm, ocaml-variants.5.3.0+options,ocaml-option-static, true, true, t...	15m 8s
build-rewatch (macos-14, aarch64-apple-darwin, darwin-arm64)	1m 0s
build-compiler (macos-13, 5.3.0, true, darwin-x64)	27m 11s
build-rewatch (ubuntu-24.04, x86_64-unknown-linux-musl, linux-x64)	1m 24s
build-compiler (macos-14, 5.3.0, true, darwin-arm64)	16m 23s
build-rewatch (ubuntu-24.04-arm, aarch64-unknown-linux-musl, linux-arm64)	2m 46s
build-compiler (windows-latest, 5.3.0, true, win32-x64)	5m 3s
build-rewatch (windows-latest, x86_64-pc-windows-gnu, win32-x64)	5m 33s
build-compiler (ubuntu-24.04, ocaml-variants.5.2.1+options,ocaml-option-static)	16m 50s
build-compiler (ubuntu-24.04, ocaml-variants.5.0.0+options,ocaml-option-static)	16m 19s
build-compiler (ubuntu-24.04, ocaml-variants.4.14.2+options,ocaml-option-static)	16m 24s
pkg-pr-new	52s
installationTest (macos-13, darwin-x64)	22s
installationTest (macos-14, darwin-arm64)	18s
installationTest (ubuntu-24.04, linux-x64)	13s
installationTest (ubuntu-24.04-arm, linux-arm64)	27s
installationTest (windows-latest, win32-x64)	1m 13s
publish	0s
	2h 26m 17s

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