vapi: Removed src/vapi/ which was required for very old versions of gio-2.0.vapi

build: depend on Vala 0.16.0 as a minimum to cater for this change so we don't
carry around an old version of the GIO bindings...

https://bugzilla.gnome.org/show_bug.cgi?id=706003
Merge branch 'remove-old-gio-vapi'