refactor: hide or remove unused code. #407

Job	Run time
Cross Build Only (x86_64-unknown-freebsd)	48s
Android Build Only (armv7-linux-androideabi)	1m 9s
Android Build Only (aarch64-linux-android)	1m 8s
check_semver	1m 7s
Checking fmt	26s
clippy_check	1m 39s
Cross Test (i686-unknown-linux-gnu)	1m 27s
Checking docs	53s
codespell	6s
Minimal Supported Rust Version	59s
cargo deny	29s
CI Test Suite / Tests (windows-latest, stable, default, x86_64-pc-windows-msvc)	2m 0s
CI Test Suite / Tests (windows-latest, stable, all, x86_64-pc-windows-msvc)	1m 55s
CI Test Suite / Tests (ubuntu-latest, stable, all)	1m 31s
CI Test Suite / Tests (macOS-arm-latest, stable, none)	1m 31s
CI Test Suite / Tests (macOS-arm-latest, stable, all)	1m 41s
CI Test Suite / Tests (windows-latest, stable, none, x86_64-pc-windows-msvc)	1m 55s
CI Test Suite / Tests (ubuntu-latest, stable, default)	1m 9s
CI Test Suite / Tests (ubuntu-latest, stable, none)	1m 32s
CI Test Suite / Tests (macOS-arm-latest, stable, default)	1m 32s
	24m 57s

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