Don't include unreachable files in local docs to save space

#20714 (closed) was about files from the website that are installed into Tails but not linked to in the local docs.

Example: mac.mp4 is 719K

Simply removing mac.mp4 alone would already save us far more space than removing aircrack-ng did. And there are more unused files in the Tails local docs.

Proof that mac.mp4 is unused:

``` $ find -type f -exec grep -iF -- mac.mp4 {} +; ./doc/first_steps/start/mac.ca.html: ./doc/first_steps/start/mac.de.html: ./doc/first_steps/start/mac.en.html: ./doc/first_steps/start/mac.es.html: ./doc/first_steps/start/mac.fr.html: ./doc/first_steps/start/mac.it.html: ./doc/first_steps/start/mac.pt.html: ./doc/first_steps/start/mac.ru.html: ./doc/upgrade/clone.ca.html: ./doc/upgrade/clone.de.html: ./doc/upgrade/clone.en.html: ./doc/upgrade/clone.es.html: ./doc/upgrade/clone.fr.html: ./doc/upgrade/clone.it.html: ./doc/upgrade/clone.pt.html: ./doc/upgrade/clone.ru.html: ./doc/upgrade/linux.ca.html: ./doc/upgrade/linux.de.html: ./doc/upgrade/linux.en.html: ./doc/upgrade/linux.es.html: ./doc/upgrade/linux.fr.html: ./doc/upgrade/linux.it.html: ./doc/upgrade/linux.pt.html: ./doc/upgrade/linux.ru.html: ./doc/upgrade/mac.ca.html: ./doc/upgrade/mac.de.html: ./doc/upgrade/mac.en.html: ./doc/upgrade/mac.es.html: ./doc/upgrade/mac.fr.html: ./doc/upgrade/mac.it.html: ./doc/upgrade/mac.pt.html: ./doc/upgrade/mac.ru.html: ./doc/upgrade/tails.ca.html: ./doc/upgrade/tails.de.html: ./doc/upgrade/tails.en.html: ./doc/upgrade/tails.es.html: ./doc/upgrade/tails.fr.html: ./doc/upgrade/tails.it.html: ./doc/upgrade/tails.pt.html: ./doc/upgrade/tails.ru.html: ./doc/upgrade/windows.ca.html: ./doc/upgrade/windows.de.html: ./doc/upgrade/windows.en.html: ./doc/upgrade/windows.es.html: ./doc/upgrade/windows.fr.html: ./doc/upgrade/windows.it.html: ./doc/upgrade/windows.pt.html: ./doc/upgrade/windows.ru.html: ./install/clone/mac.ca.html: ./install/clone/mac.de.html: ./install/clone/mac.en.html: ./install/clone/mac.es.html: ./install/clone/mac.fr.html: ./install/clone/mac.it.html: ./install/clone/mac.pt.html: ./install/clone/mac.ru.html: ./install/clone/pc.ca.html: ./install/clone/pc.de.html: ./install/clone/pc.en.html: ./install/clone/pc.es.html: ./install/clone/pc.fr.html: ./install/clone/pc.it.html: ./install/clone/pc.pt.html: ./install/clone/pc.ru.html: ./install/expert.ca.html: ./install/expert.de.html: ./install/expert.en.html: ./install/expert.es.html: ./install/expert.fr.html: ./install/expert.it.html: ./install/expert.pt.html: ./install/expert.ru.html: ./install/inc/steps/mac_startup_disks.inline.ca.html: ./install/inc/steps/mac_startup_disks.inline.de.html: ./install/inc/steps/mac_startup_disks.inline.en.html: ./install/inc/steps/mac_startup_disks.inline.es.html: ./install/inc/steps/mac_startup_disks.inline.fr.html: ./install/inc/steps/mac_startup_disks.inline.it.html: ./install/inc/steps/mac_startup_disks.inline.pt.html: ./install/inc/steps/mac_startup_disks.inline.ru.html: ./install/inc/steps/restart_first_time.inline.ca.html: ./install/inc/steps/restart_first_time.inline.de.html: ./install/inc/steps/restart_first_time.inline.en.html: ./install/inc/steps/restart_first_time.inline.es.html: ./install/inc/steps/restart_first_time.inline.fr.html: ./install/inc/steps/restart_first_time.inline.it.html: ./install/inc/steps/restart_first_time.inline.pt.html: ./install/inc/steps/restart_first_time.inline.ru.html: ./install/linux.ca.html: ./install/linux.de.html: ./install/linux.en.html: ./install/linux.es.html: ./install/linux.fr.html: ./install/linux.it.html: ./install/linux.pt.html: ./install/linux.ru.html: ./install/mac.ca.html: ./install/mac.de.html: ./install/mac.en.html: ./install/mac.es.html: ./install/mac.fr.html: ./install/mac.it.html: ./install/mac.pt.html: ./install/mac.ru.html: ./install/windows.ca.html: ./install/windows.de.html: ./install/windows.en.html: ./install/windows.es.html: ./install/windows.fr.html: ./install/windows.it.html: ./install/windows.pt.html: ./install/windows.ru.html: ```

refs #21006 (closed)