Remove OPpCONST_FOLDED

Remove OPpCONST_FOLDED

Now that we have op->op_folded, we don’t need OPpCONST_FOLDED any
more.  In removing it, I modified B::Concise to output op_folded the
way OPpCONST_FOLDED was output before, since it can be helpful to have
it when reading op dumps.