The last user of dev_priv->no_aux_handshake was removed in commit
3cf2efb1 ("Revert "drm/i915/dp: use VBT provided eDP params if
available""). Finally remove the leftovers.

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: NChris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: NJani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/f1f0830bb43ddc6857d6a43e51c14b2f0c58c4e0.1565271681.git.jani.nikula@intel.com