Finally we are able to remove this class entirely, along with the last
vestiges of it's use. I've also removed some legacy files that were only
used for windows XP support.
BUG=webrtc:7035
Review-Url: https://codereview.webrtc.org/2790533002
Cr-Commit-Position: refs/heads/master@{#17480}
Since this is on Windows only, I'm also using the CriticalSectionWrapper and ConditionVariableWrapper Windows types directly which allows us to skip 3 extra heap allocations. It also helps with the removal of the 'friend' relationship between ConditionVariableWrapper and CriticalSectionWrapper, which is causing headaches on Mac.
BUG=
Review URL: https://codereview.webrtc.org/1595983002
Cr-Commit-Position: refs/heads/master@{#11300}