Clean-up content sandboxing code for Tor Browser on Windows

Jacek wrote back then a PoC to get the Tor Browser content sandbox compiled for Windows. We should go thoroughly over the that code and clean it up.

We already shipped two fix up patches to the original patch:

https://gitweb.torproject.org/tor-browser.git/commit/?h=tor-browser-52.3.0esr-7.5-2&id=2354d122644d82df54d655ece5b42bdfa4cf38f8 https://gitweb.torproject.org/tor-browser.git/commit/?h=tor-browser-52.4.0esr-7.5-1&id=0a9793458e9ddd5c7742d3ceb250125c52e8bf86

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