[iceweasel][icedove] Branding files are in plain tar archive despite xz file extension
The tar archive for branding files (iceweasel_52.0-1.branding.tar.xz) is actually a plain tar archive despite the xz file extension. While this doesn't affect the resulting Parabola package, it may confuse some tools1 if the file is used elsewhere. It also increased the size of the archive by 10 times compared to the previous version.
: For example, Gentoo's Portage will fail to automatically extract the file if it were used in an ebuild.