xsession: drop VDPAU
xsession: drop VDPAU

The test had to be updated as all my devices, apart from my old desktop,
have a Intel iGPU. So `va_gl` should be the default, but as there is to
my knowledge no VDPAU-only program, I can better just drop the test
altogether.

paretje/dotfiles,paretje/dotfiles,paretje/dotfiles,paretje/dotfiles,paretje/dotfiles