(genitem, ship, plane, land): Remove unused member sell & equivalents.

(genitem_ca, ship_ca, plane_ca, land_ca): Remove selector "sell".
(comstr, trdstr): Members trd_price, com_price have no effect.  Use
them instead of trd_maxprice, com_maxprice and remove the latter.
(commodity_ca, trade_ca): Remove selector "maxprice".

src/lib/commands/rese.c

@@ -142,8 +142,6 @@ rese(void)
     comm.com_price = price;
     (void)time(&now);
     comm.com_markettime = now;
-    if ((int)price < comm.com_maxprice)
-	comm.com_maxprice = (int)price;
     if (!putcomm(number_set, &comm)) {
 	pr("Problems with the commodities file, Call the Deity\n");
 	return RET_OK;