crypto/x509: fix CreateCRL for Ed25519 CAs

[lorenz]

This makes Ed25519 certificates work for CreateCRL(). This previously
failed (panic: crypto: requested hash function #0 is unavailable) because
the hash could not be skipped, but Ed25519 uses no hash.

A similar fix has been applied in a few other places when Ed25519 was added
when Ed25519 certificates were originally introduced, but was missed
here.

Change-Id: I16fcfcd53ba3bb8f773e5de972b8fedde1f6350e

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This PR (HEAD: bf7f145) has been imported to Gerrit for code review.

Please visit https://go-review.googlesource.com/c/go/+/204046 to see it.

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Message from Lorenz Brun:

Patch Set 1:

BTW this has been submitted on GitHub because Gerrit really doesn't like me adding private keys for the tests (![remote rejected] HEAD -> refs/for/master (found a private key)). There does not seem to be a documented workaround and the given command line argument (-o nokeycheck) does not work for submissions. So I've just used GitHub which doesn't have the same restrictions. It's a cool feature but the override should really work.

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Message from Gobot Gobot:

Patch Set 1:

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Message from Lorenz Brun:

Patch Set 2: Commit message was updated.

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Message from Brad Fitzpatrick:

Patch Set 3: Run-TryBot+1

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Message from Gobot Gobot:

Patch Set 3:

TryBots beginning. Status page: https://farmer.golang.org/try?commit=532980eb

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Message from Gobot Gobot:

Patch Set 3: TryBot-Result+1

TryBots are happy.

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Message from Lorenz Brun:

Patch Set 3:

A friendly ping

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Message from Filippo Valsorda:

Patch Set 3: Code-Review+2

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Message from Filippo Valsorda:

Patch Set 3:

Thank you, good catch.

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This PR is being closed because golang.org/cl/204046 has been merged.