drm: kill some unused DRM_PROC macros from drmP.h

i915_gem_proc.c appears to have been the last user of the DRM_PROC_*
macros, and it has gone away.  The macros should die as well.

Signed-off-by: Andres Salomon <dilinger@collabora.co.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Dave Airlie <airlied@redhat.com>