i965: Drop "Destination Element Offset" from Ironlake SGVs.

i965: Drop "Destination Element Offset" from Ironlake SGVs.

The Ironlake documentation is terrible, so it's unclear whether or not
this field exists there.  It definitely doesn't exist on Sandybridge
and later.  It definitely does exist on G45.

We haven't been setting it for our normal vertex attributes - just
the SGVs (VertexID, InstanceID, BaseVertex, BaseInstance, DrawID).
We should be consistent.  My guess is that it isn't necessary and
doesn't exist - this patch drops it from the SGVs elements, making
them follow the behavior of most attributes.

Reviewed-by: Rafael Antognolli <rafael.antognolli@intel.com>