Remove thiserror and smallvec deps #2285

Job	Run time
Test	49s
Test	24s
Test (charset)	37s
build_versions (stable)	30s
Test (charset)	25s
cargo-deny (aarch64-apple-ios)	23s
Test (cookies)	40s
build_versions (beta)	29s
Test (cookies)	35s
cargo-deny (aarch64-linux-android)	19s
build_versions (1.67.0)	25s
Test (socks-proxy)	45s
Test (socks-proxy)	24s
cargo-deny (i686-pc-windows-gnu)	19s
Test (gzip)	36s
Test (gzip)	23s
cargo-deny (i686-pc-windows-msvc)	16s
Docs	19s
Test (brotli)	40s
cargo-deny (i686-unknown-linux-gnu)	20s
cargo-deny (wasm32-unknown-unknown)	20s
Test (json)	36s
cargo-deny (x86_64-apple-darwin)	19s
Lint	33s
Test (native-tls)	57s
cargo-deny (x86_64-apple-ios)	20s
Test (brotli)	28s
cargo-deny (x86_64-pc-windows-gnu)	18s
Test (json)	35s
cargo-deny (x86_64-pc-windows-msvc)	19s
Test (native-tls)	41s
cargo-deny (x86_64-unknown-linux-gnu)	18s
cargo-deny (x86_64-unknown-redox)	18s
	15m 40s

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