Do not install tails-installer to $PATH
As some command line options for tails-installer are not currently functional, we should avoid installing tails-installer to $PATH and instead treat it as a mere helper for tails-installer-launcher. That is, do not install to /usr/bin.
We could do that via the packaging or upstream. And this will probably be reverted once we fix #8549 (closed)
Feature Branch: 451f:tails/jessie
Parent Task: #8549 (closed)