Remove transport deprecated method CancelRequest

[beornf]

As mentioned in issue #271 the CancelRequest method is deprecated and was replaced with context cancellation in Go 1.7. This should do away with the need to store a map of modified requests.

My main motivation for this code cleanup is to allow returning a writable body response in the transport https://golang.org/src/net/http/response.go#L344 needed in websockets and other protocols protected by oauth2.

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This PR (HEAD: c36076d) has been imported to Gerrit for code review.

Please visit https://go-review.googlesource.com/c/oauth2/+/209518 to see it.

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Message from Brad Fitzpatrick:

Patch Set 1:

(1 comment)

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Message from Beorn Facchini:

Patch Set 1:

I also noticed patch https://go-review.googlesource.com/c/oauth2/+/121438 addresses the same issue in Gerrit. Should I continue with this patch?

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Message from Brad Fitzpatrick:

Patch Set 1:

Patch Set 1:

I also noticed patch https://go-review.googlesource.com/c/oauth2/+/121438 addresses the same issue in Gerrit. Should I continue with this patch?

Oh, right. I guess we should just let that one finish. Or I can take it over.

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This PR is being closed because golang.org/cl/209518 has been abandoned.

Done by https://go-review.googlesource.com/c/oauth2/+/121438