This makes more of the gcc spurious warning:
../../src/hb-null.hh:53:39: warning: enum constant in boolean context [-Wint-in-bool-context]
But not going to let that defeat correct code. Type to switch to clang
as my main compiler...
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.