[X86] Remove a DCI.isBeforeLegalize() call from combineVSelectWithAllOnesOrZeros.

This was blocking isTypeLegal call so that we could do a particular
transform on illegal types before type legalization. But the we
create a target specific node using that type. We shouldn't do
that if the type isn't legal. So I think we should just always
make sure the type is legal.

I suspect that in order to get the condition VT to not be a vector
of i1 we already completed type legalization anyway so this probably
doesn't matter much in practice.