vaapivideobufferpool: remove allocation_vinfo private attribute
vaapivideobufferpool: remove allocation_vinfo private attribute

There is no need to keep this attribute internally since it is
already managed by the allocator.

https://bugzilla.gnome.org/show_bug.cgi?id=783599

ceyusa/gstreamer-vaapi,ceyusa/gstreamer-vaapi,GStreamer/gstreamer-vaapi,GStreamer/gstreamer-vaapi