main: Remove clutter / cogl option groups

Neither of these groups are too useful, and all the switches useful
for debugging can also be controlled by envvars.
wayland: Remove is_native from seat

We can easily do this with a Clutter backend check instead...
monitor: Kill off another use of is_native
cursor-tracker: Kill off the last user of is_native
wayland: Kill meta_wayland_compositor_is_native

It's unused. Squash the remaining functionality, setting the DRM FD,
into the main path.