vaapipostproc: removed unused parameter
vaapipostproc: removed unused parameter

Removed caps parameter from gst_vaapipostproc_transform_caps_impl()
helper function since the it is not used.

https://bugzilla.gnome.org/show_bug.cgi?id=785706

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