build: Fix banshee-hyena-gui.pc to remove old Mono.Cairo references

The pkgconfig file that banshee generates for its own Hyena assemblies
where still being linked to old Mono.Cairo and in addition the new
cairo-sharp. This allows GTK3-compatible Banshee-Community-Extensions to
build properly with the new version of the toolkit.

Signed-off-by: Bertrand Lorentz <bertrand.lorentz@gmail.com>