Test suite: remove obsolete scenario

This scenario tested 2 things:

 - Starting Tails installed from the (hybrid) ISO image copied bit-by-bit to the
   USB stick: we don't support this since January 2019 anymore.

 - Tails Installer is able to reinstall a USB stick installed from the (hybrid)
   ISO image copied bit-by-bit, by cloning another running Tails. That's
   a useful feature for users who are migrating a USB stick installed in 2018 or
   earlier, but after almost 1.5 years of transition time, IMO we've reached the
   point when it's not worth spending almost 12 minutes (more than 25% of the
   usb_install.feature) on every Jenkins test suite run, just to ensure we did
   not break this scenario. Given the low amount of work we're putting into
   Tails Installer these days, the risk of regression is quite limited anyway.