clean up code #317

Job	Run time
Bitrot check	1m 39s
Build target wasm32-unknown-unknown	2m 42s
Book tests	2m 16s
Build target wasm32-wasi	2m 32s
Rustfmt	15s
Intra-doc links	2m 19s
Test on i686-unknown-linux-gnu	21m 58s
Test on i686-unknown-linux-gnu with beta features	21m 38s
Test on ubuntu-latest	11m 2s
Test on i686-unknown-linux-gnu with nightly features	22m 57s
Test on windows-latest	14m 50s
Test on macOS-latest	10m 37s
Test on ubuntu-latest with beta features	10m 38s
Test on windows-latest with beta features	14m 37s
Test on macOS-latest with beta features	10m 31s
Test on ubuntu-latest with nightly features	11m 25s
Test on windows-latest with nightly features	15m 18s
Test on macOS-latest with nightly features	11m 6s
	3h 8m 20s

Provide feedback