(mult, player_coms): Command `mult' is disabled since 4.0.0 ('96), and

its code is obviously not in working order.  Remove.
(minmult, maxmult, configkeys): Unused configuration parameters,
remove.
(tradedesc): Remove code related to mult that had no effect.
(multread, commread, commwrite, commamt, commset, multset, commprice):
Dangerous, because code bypasses ef_read() & friends, remove.
(diss): Commodity cleanup uses the above, remove.  Command is disabled
and unlikely to work anyway.

include/commands.h

@@ -142,7 +142,6 @@ int mobq(void);
 int mobupdate(void);
 int morale(void);
 int move(void);
-int mult(void);
 int multifire(void);
 int name(void);
 int nati(void);