Remove unused rustversion dependency of axum-core #5781

Job	Run time
check	43s
check-docs	25s
cargo-hack	2m 47s
cargo-public-api-crates (axum-core)	21s
cargo-public-api-crates (axum)	39s
dependencies-are-sorted	3s
cargo-public-api-crates (axum-extra)	35s
cargo-deny check (bans licenses sources)	27s
cargo-deny check (advisories)	28s
Spell Check with Typos	6s
cargo-public-api-crates (axum-macros)	21s
test-nightly	1m 1s
test-docs	59s
test-versions (beta)	1m 5s
test-versions (stable)	1m 10s
armv5te-unknown-linux-musleabi	36s
wasm32-unknown-unknown	20s
test-msrv	2m 14s
	14m 20s

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