make damage type -> sound type DRY

And while I'm at it, resolve a TODO note and remove a bunch of unnecessary 0s

src/game/boe.townspec.cpp

@@ -77,7 +77,7 @@ bool run_trap(short pc_num,eTrapType trap_type,short trap_level,short diff) {
 			for(short i = 0; i < num_hits; i++) {
 				add_string_to_buf("  A knife flies out!");
 				r1 = get_ran(2 + univ.town->difficulty / 14,1,10);
-				damage_pc(disarmer,r1,eDamageType::WEAPON,eRace::UNKNOWN,0);
+				damage_pc(disarmer,r1,eDamageType::WEAPON,eRace::UNKNOWN);
 			}
 			break;