Merge branch 'purge-kubuntu-firefox-installer' into 'master'

Purge kubuntu-firefox-installer

This is a package preinstalled in Kubuntu that creates a menu entry to install the package "firefox." One can easily install abrowser or icecat using a package manager, and kubuntu-firefox-installer doesn't work in Trisquel anyway, so it's best to remove it.

See merge request !15