drm/i915/dvo: Remove unused panel_wants_dither

intel_dvo.panel_wants_dither is only set but never used.
We can't do dithering on the gmch side anyway since the
dithering logic is part of the integrated LVDS port and
not available for other output types.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221118105525.27254-2-ville.syrjala@linux.intel.com


Reviewed-by: Jani Nikula <jani.nikula@intel.com>