Bug#886063: libgnomecanvas: Don't release with Buster

[Borden Rhodes]

I apologise. The relevant post is
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=885777#22:

"Uh, wait... the mailing list post from October 2017 announcing the
deprecation and removal of libgnome and libgnomeui and other related
libraries didn't even list libgnomecanvas among the libraries to be
removed, or xournal among the affected packages -- perhaps showing
awareness that libgnomecanvas is in fact not related to libgnome in
any way.  Could it be that someone got overzealous and decided to
remove libgnomecanvas for no good reason?  Perhaps that can still be
undone?"