Bug#975374: [Pkg-sugar-devel] Bug#975374: sugar-calculate-activity: reproducible builds: Embeds build path in .desktop file

[James Cameron]

Upstream bug
https://github.com/sugarlabs/sugar-toolkit-gtk3/issues/453

sugar-toolkit-gtk3 does not provide DESTDIR support yet, and
cdbs passes DEB_DESTDIR as PREFIX.