Plane: reset VTOL takeoff if not armed

we need to reset the takeoff target position while disarmed so we
don't use spurious position information from before we get good GPS
lock.

also remove the "Resetting previous waypoint" message as it doesn't
provide useful information and is just a distraction (it would be
printed continuously while waiting for arming with this PR)

ArduPlane/commands.cpp

@@ -51,7 +51,6 @@ void Plane::set_next_WP(const struct Location &loc)
     // location as the previous waypoint, to prevent immediately
     // considering the waypoint complete
     if (current_loc.past_interval_finish_line(prev_WP_loc, next_WP_loc)) {
-        gcs().send_text(MAV_SEVERITY_NOTICE, "Resetting previous waypoint");
         prev_WP_loc = current_loc;
     }
 

ArduPlane/quadplane.cpp

@@ -3421,9 +3421,10 @@ bool QuadPlane::verify_vtol_takeoff(const AP_Mission::Mission_Command &cmd)
 
     const uint32_t now = millis();
 
-    // reset takeoff start time if we aren't armed, as we won't have made any progress
+    // reset takeoff if we aren't armed
     if (!hal.util->get_soft_armed()) {
-        takeoff_start_time_ms = now;
+        do_vtol_takeoff(cmd);
+        return false;
     }
 
     if (now - takeoff_start_time_ms < 3000 &&