i965/gen6: Remove state flagging on BRW_NEW_CURBE_OFFSETS.

i965/gen6: Remove state flagging on BRW_NEW_CURBE_OFFSETS.

That flag was leftover from gen4, where brw_curbe.c is choosing ranges
of the CURBE space for constants to live in, and the unit state tells
where to load them from.  That's not the case on gen6 -- we don't set
this flag (since constants aren't in the URB), nor do we have any
state like that to upload.