drm/i915: remove left over dead code

ae80152d ("drm/i915: Rewrite VLV/CHV
watermark code") removed everything that would have used those vars.

Signed-off-by: Eric Engestrom <eric.engestrom@imgtec.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: http://patchwork.freedesktop.org/patch/msgid/1456763047-28828-1-git-send-email-eric.engestrom@imgtec.com