Use header constants #2370

Job	Run time
build_versions (stable)	21s
Test	44s
build_versions (beta)	16s
Test	31s
Test (charset)	46s
build_versions (1.67.0)	22s
Test (charset)	37s
Test (cookies)	53s
cargo-deny (aarch64-apple-ios)	21s
Test (cookies)	35s
Test (socks-proxy)	49s
cargo-deny (aarch64-linux-android)	22s
Docs	36s
Test (socks-proxy)	35s
Test (gzip)	46s
cargo-deny (i686-pc-windows-gnu)	18s
Test (gzip)	35s
Test (brotli)	48s
cargo-deny (i686-pc-windows-msvc)	19s
Test (brotli)	34s
Test (json)	54s
cargo-deny (i686-unknown-linux-gnu)	22s
Lint	37s
Test (json)	35s
Test (native-tls)	53s
cargo-deny (wasm32-unknown-unknown)	21s
Test (native-tls)	43s
cargo-deny (x86_64-apple-darwin)	18s
cargo-deny (x86_64-apple-ios)	20s
cargo-deny (x86_64-pc-windows-gnu)	20s
cargo-deny (x86_64-pc-windows-msvc)	19s
cargo-deny (x86_64-unknown-linux-gnu)	23s
cargo-deny (x86_64-unknown-redox)	19s
	17m 32s

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