Remove doc `html_root_url` #242

Job	Run time
Check MSRV and minimal-versions	1m 44s
clippy	15s
nostd_build (1.63.0, thumbv6m-none-eabi)	1m 19s
miri	2m 33s
nostd_build (stable, thumbv6m-none-eabi)	17s
tests (1.63.0)	1m 49s
tests (stable, arbitrary)	33s
tests (stable, quickcheck)	39s
tests (stable, rayon)	44s
tests (stable, rustc-rayon)	46s
tests (stable, serde)	40s
tests (stable, std)	41s
tests (beta)	33s
tests (nightly, test build benchmarks)	35s
	13m 8s

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