Remove `thiserror` from `bevy_pbr` #50560

Job	Run time
build (windows-latest)	11m 23s
check-doc	12m 6s
build (ubuntu-latest)	4m 35s
ci	4m 40s
miri	9m 51s
build (macos-latest)	4m 23s
run-examples-macos-metal	8m 9s
toml	1m 54s
typos	9s
check-bevy-internal-imports	8s
check-missing-examples-in-docs	36s
check-missing-features-in-docs	29s
markdownlint	1m 3s
check-compiles	6m 44s
msrv	1m 46s
build-wasm	1m 41s
build-wasm-atomics	1m 45s
	1h 11m 22s

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