test: clean up run.go
test: clean up run.go

• Inline check function because it's more readable.
• Delete toolPath because it was unused.
• Use strings.TrimPrefix because it's simpler.
• Remove out variable because its value was unused.
• Rename serr to err because it's more consistent.

Change-Id: I084fb4f8b399578834d5eea29a673c386cf3a357
Reviewed-on: https://go-review.googlesource.com/c/go/+/218701
Run-TryBot: Dmitri Shuralyov <d181b7fea0ec87c86ba5a890ab716db52498e3ba@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>
Reviewed-by: Hajime Hoshi <1c55649263e1aefbe86bfa40d3d8351033a4d83f@gmail.com>

cloudflare/go,CAFxX/go,CAFxX/go,CAFxX/go,cloudflare/go,akutz/go,golang/go,nawawi/go,nawawi/go,golang/go,cloudflare/go,CAFxX/go,CAFxX/go,nawawi/go,nawawi/go,golang/go,golang/go,nawawi/go,cloudflare/go,CAFxX/go,cloudflare/go,golang/go,akutz/go,akutz/go,cloudflare/go,akutz/go,akutz/go,nawawi/go,cloudflare/go,CAFxX/go,akutz/go,nawawi/go,nawawi/go,golang/go,golang/go,cloudflare/go,akutz/go,CAFxX/go,akutz/go,golang/go