Drop redundant or wrong `Requires feature` documentation #1689

Job	Run time
Docs	45s
cargo-deny (aarch64-apple-ios)	24s
Lint	39s
Test	1m 5s
cargo-deny (aarch64-linux-android)	33s
Test (json)	1m 16s
cargo-deny (i686-pc-windows-gnu)	24s
Test (charset)	1m 16s
cargo-deny (i686-pc-windows-msvc)	27s
Test (cookies)	1m 17s
cargo-deny (i686-unknown-linux-gnu)	31s
Test (socks-proxy)	1m 5s
cargo-deny (wasm32-unknown-unknown)	27s
Test (native-certs)	1m 4s
cargo-deny (x86_64-apple-darwin)	24s
Test (gzip)	1m 11s
cargo-deny (x86_64-apple-ios)	24s
Test (brotli)	1m 17s
cargo-deny (x86_64-pc-windows-gnu)	26s
Test (http-interop)	1m 8s
cargo-deny (x86_64-pc-windows-msvc)	30s
Test (tls)	1m 29s
cargo-deny (x86_64-unknown-linux-gnu)	24s
Test (tls, json)	1m 27s
Test (tls, charset)	1m 30s
cargo-deny (x86_64-unknown-redox)	27s
Test (tls, cookies)	1m 31s
Test (tls, socks-proxy)	1m 24s
Test (tls, native-certs)	1m 18s
Test (tls, gzip)	1m 18s
Test (tls, brotli)	3m 23s
Test (tls, http-interop)	1m 31s
Test (native-tls)	1m 17s
Test (native-tls, json)	1m 41s
Test (native-tls, charset)	1m 28s
Test (native-tls, cookies)	1m 42s
Test (native-tls, socks-proxy)	1m 19s
Test (native-tls, native-certs)	1m 20s
Test (native-tls, gzip)	1m 16s
Test (native-tls, brotli)	1m 20s
Test (native-tls, http-interop)	1m 21s
	44m 59s

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