Dropped gnome-calculator and gnome-music

[Colin Walters <walters verbum org>]

gnome-calculator was hitting a strange build issue we think may be due
to the GOption changes in GLib impacting the gtksourceview build:
http://build.gnome.org/continuous/buildmaster/builds/2014/10/20/18/build/log-gnome-calculator.txt

gnome-music was hitting libmediaart issues (need to check whether
they're parallel installable).

For now though I just removed both due to lack of debugging time on my
part - if someone would be willing to try to revive them please feel
free to dive in and when they're working readd to the manifest.