windows/mkwinsyscall: remove errnoERROR_IO_PENDING const

[thaJeztah]

From the looks of it, this const is redundant (but perhaps there's something I'm overlooking 😅)

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Message from Ian Lance Taylor:

Patch Set 1:

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Message from Sebastiaan van Stijn:

Patch Set 1:

(1 comment)

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Message from Ian Lance Taylor:

Patch Set 1:

(1 comment)

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Please don’t reply on this GitHub thread. Visit golang.org/cl/441439.
After addressing review feedback, remember to publish your drafts!