Plane: bugfix: never reset auto_state.sink_rate

ArduPlane/commands_logic.cpp

@@ -15,9 +15,6 @@ bool Plane::start_command(const AP_Mission::Mission_Command& cmd)
 
     // special handling for nav vs non-nav commands
     if (AP_Mission::is_nav_cmd(cmd)) {
-        // set land_complete to false to stop us zeroing the throttle
-        auto_state.sink_rate = 0;
-
         // set takeoff_complete to true so we don't add extra elevator
         // except in a takeoff
         auto_state.takeoff_complete = true;