drm/i915: Remove inactive/active list from debugfs

These two files (i915_gem_active, i915_gem_inactive) no longer give
pertinent information since active/inactive tracking is per-vm and so we
need the information per-vm. They are obsolete so remove them.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1471254551-25805-4-git-send-email-chris@chris-wilson.co.uk