Remove unused stuff from Bsb_exception #5144

Job	Run time
build-rewatch (macos-13, x86_64-apple-darwin)	20s
build-rewatch (macos-14, aarch64-apple-darwin)	14s
build-compiler (ubuntu-latest, ocaml-variants.5.2.0+options,ocaml-option-static, true, true, true...	1m 31s
build-rewatch (ubuntu-latest, x86_64-unknown-linux-musl)	10s
build-compiler (buildjet-2vcpu-ubuntu-2204-arm, ocaml-variants.5.2.0+options,ocaml-option-static,...	2m 58s
build-rewatch (buildjet-2vcpu-ubuntu-2204-arm, aarch64-unknown-linux-musl)	15s
build-compiler (macos-13, 5.2.0, true)	3m 30s
build-rewatch (windows-latest, x86_64-pc-windows-gnu)	21s
build-compiler (macos-14, 5.2.0, true)	1m 58s
build-compiler (windows-latest, 5.2.0, true)	3m 17s
build-compiler (ubuntu-latest, ocaml-variants.5.0.0+options,ocaml-option-static)	1m 40s
build-compiler (ubuntu-latest, ocaml-variants.4.14.2+options,ocaml-option-static)	1m 43s
build-compiler (ubuntu-latest, ocaml-variants.4.13.0+options,ocaml-option-static)	1m 38s
package	0s
installationTest	0s
publish	0s
	19m 35s

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