No other shaper will need shape_plan_data, by definition. So, remove
abstraction layer and always create hb_ot_shape_plan_t as part of
hb_shape_plan_t.
Newer compilers / language allows structs with constructor in union.
So, this was not actually testing anything. Indeed, the recent
change in DISALLOW_COPY *is* making some of our types non-POD.
That broke some bots.
Just remove this since it wasn't doing much, and I'd rather have
DISALLOW_COPY.
Behdad Esfahbod