io/ioutil: don't check for short write in WriteFile
io/ioutil: don't check for short write in WriteFile

*os.File already does it.

Fixes #33064

Change-Id: I3edf0a31bf6d6e5023f47f01ebc92ed057357278
GitHub-Last-Rev: e6a5ba45d7e74def668adf145f46387ef27f5d28
GitHub-Pull-Request: golang/go#33065
Reviewed-on: https://go-review.googlesource.com/c/go/+/185857
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>
Run-TryBot: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

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