Install tsocks from testing once it is back in Stretch
I've NMU'ed it to Debian to fix https://bugs.debian.org/769343, and uploaded to our
feature-stretch so that we have it until it makes it into Debian testing.
Use torsocks to torify Git, and drop tsocks entirely.
tsocks has been unmaintained for years in Debian, and is not in testing
at the moment.
Since we dropped ttdnsd, the only use case for tsocks was torifying Git.
But thanks to torsocks 2.1's AllowOutboundLocalhost we can now use torsocks to
torify Git without breaking Git-over-SSH. See 3922b0b2 for the previous
iteration of this.