identity: Remove.

identity: Remove.

It's unmaintained, and most likely broken: I use trace driver every now
and then, and everytime I do I need to fix it up.

It's also unused: identity_screen_create is never called.

Above all, it's dead weight: if identity driver had the infrastructure
for other pass-through drivers (like trace and rbug), then it would make
sense on its own right.  But as it is implemmented, it's just another
driver to (forget) to update whenever there is a gallium interface
change.

Reviewed-by: Marek Olšák <marek.olsak@amd.com>