(PUP-2563) Remove an optimization for earlier ruby versions

The comment suggests this optimization is for <= 1.8.7, but the
code was for < 1.9.3, so there's a little ambiguity around whether
this would have use for 1.9 versions before 1.9.3. But carrying
an optimization for early 1.9's doesn't make a lot of sense anyway,
so I'm just yanking this code.