The GLTextureUploadMeta implementation assumed that for each upload()
sequence, the supplied texture id is always the same as the one that
was previously cached into the underlying GstVaapiTexture. Cope with
any texture id change the expense to recreate the underlying VA/GLX
resources.
https://bugzilla.gnome.org/show_bug.cgi?id=719643
Drop obsolete GST_VAAPI_IS_xxx() helper macros since we are no longer
deriving from GObject and so those were only checking for whether the
argument was NULL or not. This is now irrelevant, and even confusing
to some extent, because we no longer have type checking.
Note: this incurs more type checking (review) but the libgstvaapi is
rather small, so this is manageable.
