fix: remove unnecessary Sized boundaries #931

Job	Run time
Test Suite	1m 48s
Check	1m 48s
Rustfmt	16s
Clippy	1m 13s
Check rustdoc intra-doc links	45s
Cross compile (powerpc64-unknown-linux-gnu)	12s
Cross compile (armv7-unknown-linux-gnueabihf)	13s
Cross compile (wasm32-unknown-unknown)	14s
Cross compile (powerpc-unknown-linux-gnu)	18s
	6m 47s

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