dhc2: implement wing tip tanks; the aircraft had 100 pounds of fuel in
each by default but the switch in the cockpit was non-functional.
* Systems/fuel.xml: new fuel flows from the wing tip tanks to the forward tank. * Nasal/dhc2.nas: delete unused code.
Authored by: lbrenta 2018-06-25
Parent: [r3318]
Child: [r3320]
