all: replace io/ioutil with io and os package

[cuishuang]

[gopherbot]

This PR (HEAD: f07ea9abc8d542a7a9c541700b080414af53dc95) has been imported to Gerrit for code review.

Please visit https://go-review.googlesource.com/c/mod/+/430799 to see it.

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[gopherbot]

Message from Bryan Mills:

Patch Set 1: Run-TryBot+1 Auto-Submit+1 Code-Review+2

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Please don’t reply on this GitHub thread. Visit golang.org/cl/430799. After addressing review feedback, remember to publish your drafts!

[gopherbot]

Message from Gopher Robot:

Patch Set 1:

(1 comment)

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[gopherbot]

Message from Gopher Robot:

Patch Set 1:

(1 comment)

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Message from Gopher Robot:

Patch Set 1: TryBot-Result-1

(1 comment)

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[gopherbot]

Message from Bryan Mills:

Patch Set 1: -Auto-Submit Code-Review+1

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[alexandear]

@cuishuang Could you close the PR because of merged #17?

[gopherbot]

This PR is being closed because golang.org/cl/430799 has been abandoned.

Subsumed by CL 462278.