Remove Windows documentation.

[david-german-tri]

This change is

[jwnimmer-tri]

FYI to any other readers, a mex -setup step got removed here also for all platforms, but it seems like a correct improvement.

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Comments from Reviewable

[jwnimmer-tri]

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Reviewed 8 of 8 files at r1.
Review status: all files reviewed at latest revision, all discussions resolved.

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Comments from Reviewable

[liangfok]

There are numerous images in https://github.com/RobotLocomotion/drake/tree/master/drake/doc/images/windows_install. Should they be removed with this PR since this PR removes the .rst file that references them?

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Review status: all files reviewed at latest revision, all discussions resolved, some commit checks pending.

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Comments from Reviewable

[david-german-tri]

Done.

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Review status: 8 of 12 files reviewed at latest revision, all discussions resolved, some commit checks pending.

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Comments from Reviewable

[jwnimmer-tri]

Reviewed 4 of 4 files at r2.
Review status: all files reviewed at latest revision, all discussions resolved, some commit checks pending.

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Comments from Reviewable

[liangfok]

+@liangfok

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Reviewed 8 of 8 files at r1, 4 of 4 files at r2.
Review status: all files reviewed at latest revision, all discussions resolved, some commit checks pending.

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Comments from Reviewable