drm: Drop unused and broken dri_library_name sysfs attribute.

The kernel shouldn't be in the business of telling user space which
driver to load.  The kernel defers mapping PCI IDs to module names
to user space and we should do the same for DRI drivers.

And in fact, that's how it does work today.  Nothing uses the
dri_library_name attribute, and the attribute is in fact broken.
For intel devices, it falls back to the default behaviour of returning
the kernel module name as the DRI driver name, which doesn't work for
i965 devices.  Nobody has ever hit this problem or filed a bug about this.

Signed-off-by: Kristian Høgsberg <krh@redhat.com>
Signed-off-by: Dave Airlie <airlied@linux.ie>