From the publishing history on Launchpad:
Removal requested on 2016-02-05.
Deleted on 2016-02-05 by Steve Langasek
(From Debian) RoQA; dead upstream; depends on gstreamer 0.10; Debian
It's a consequence of Debian deciding to remove gstreamer0.10 from their next release:
We shouldn't include GStreamer 0.10 in the next release, and only ship
the new 1.x release series. This was also suggested by the security
team a while ago.
GStreamer 0.10 is no longer maintained and supported by the upstream
project since almost 3 years now, and contains many known bugs that
are fixed in the new 1.x release series of GStreamer. Next to many bug
fixes, the new release series also contains many other improvements,
new features and a more streamlined API.
gstreamer0.10 is still available in Ubuntu 16.04's repositories, presumably because the removal in Debian happened too late in 16.04's development. However, the removal of guayadeque happened early, it was removed from Ubuntu as well.