"However, shouldn't I also be receiving another form, like a 1099-B?"
No. Planned liquidations - which this appears to be - are reported through the 1099-DIV. Such liquidations can span years so early distributions serve to reduce basis but if at some point the cumulative distributions exceed your basis you report that as a form of "sale."
"That's the compensation I received at company liquidation time.."
NO. The "compensation" - in the sense of "salaries and wages" - should have been recognized when the RSUs vested and that compensation should have been reported on the W-2. That "compensation" sets your basis for the stock and the liquidation distribution represents, in effect, the sale of that stock. I'm using the word in the "income tax" sense, not in the more general sense.
