drm: Remove IS_IRONLAKE_D()

This define hasn't been used since:

  commit cfdf1fa2
  Author: Kristian Høgsberg <krh@bitplanet.net>
  Date:   Wed Dec 16 15:16:16 2009 -0500

      drm/i915: Implement IS_* macros using static tables

Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>