tor-tsocks-mua.conf left over from Claws Mail removal

It seems that config/chroot_local-includes/etc/tor/tor-tsocks-mua.conf is present, and referenced in two design docs, while it is not used anymore. Please clean this up :)

Feature Branch: 451f:tails/feature/10737+icedove_design_doc

Parent Task: #10167 (closed)

Original created by @intrigeri on 10904 (Redmine)