Drop Windows-specific SSH code
Summary: Ref T2015. This code is only relevant when attempting to run commands on a Windows host over SSH. Since SSH on Windows is extremely fragile and hard to maintain, and WinRM is a better long-term solution, drop this code (which will end up being unused when later diffs introduce the WinRM command interface).
Test Plan: This code won't be used when D10495 lands.
Reviewers: Blessed Reviewers, epriestley
Reviewed By: Blessed Reviewers, epriestley
Subscribers: epriestley, Korvin
Maniphest Tasks: T2015
Differential Revision: https://secure.phabricator.com/D13340