Simplify flight startup time calls.

We can always estimate a startup time now. Remove the nullability from
the result, cleanup the callsites, and eliminate
TotEstimator.mission_start_time since it no longer does anything useful.

qt_ui/windows/mission/QFlightItem.py

@@ -1,8 +1,7 @@
-from PySide2.QtGui import QStandardItem, QIcon
+from PySide2.QtGui import QIcon, QStandardItem
 
-from game.ato.package import Package
 from game.ato.flight import Flight
-from game.ato.traveltime import TotEstimator
+from game.ato.package import Package
 from qt_ui.uiconstants import AIRCRAFT_ICONS
 
 
@@ -17,6 +16,4 @@ class QFlightItem(QStandardItem):
             icon = QIcon((AIRCRAFT_ICONS[self.flight.unit_type.dcs_id]))
             self.setIcon(icon)
         self.setEditable(False)
-        estimator = TotEstimator(self.package)
-        delay = estimator.mission_start_time(flight)
-        self.setText(f"{flight} in {delay}")
+        self.setText(f"{flight} in {flight.flight_plan.startup_time()}")

qt_ui/windows/mission/QPlannedFlightsView.py

@@ -4,10 +4,9 @@ from PySide2.QtCore import QItemSelectionModel, QSize
 from PySide2.QtGui import QStandardItemModel
 from PySide2.QtWidgets import QAbstractItemView, QListView
 
+from game.theater.controlpoint import ControlPoint
 from qt_ui.models import GameModel
 from qt_ui.windows.mission.QFlightItem import QFlightItem
-from game.theater.controlpoint import ControlPoint
-from game.ato.traveltime import TotEstimator
 
 
 class QPlannedFlightsView(QListView):
@@ -52,4 +51,4 @@ class QPlannedFlightsView(QListView):
 
     @staticmethod
     def mission_start_for_flight(flight_item: QFlightItem) -> timedelta:
-        return TotEstimator(flight_item.package).mission_start_time(flight_item.flight)
+        return flight_item.flight.flight_plan.startup_time()

qt_ui/windows/mission/flight/settings/FlightAirfieldDisplay.py

@@ -5,7 +5,6 @@ from PySide2.QtWidgets import QGroupBox, QLabel, QMessageBox, QVBoxLayout
 from game import Game
 from game.ato.flight import Flight
 from game.ato.flightplans.planningerror import PlanningError
-from game.ato.traveltime import TotEstimator
 from qt_ui.models import PackageModel
 from qt_ui.widgets.QLabeledWidget import QLabeledWidget
 from qt_ui.widgets.combos.QArrivalAirfieldSelector import QArrivalAirfieldSelector
@@ -58,9 +57,7 @@ class FlightAirfieldDisplay(QGroupBox):
             # handler may be called for a flight whose package has been canceled, which
             # is an invalid state for calling anything in TotEstimator.
             return
-        estimator = TotEstimator(self.package_model.package)
-        delay = estimator.mission_start_time(self.flight)
-        self.departure_time.setText(f"At T+{delay}")
+        self.departure_time.setText(f"At T+{self.flight.flight_plan.startup_time()}")
 
     def set_divert(self, index: int) -> None:
         old_divert = self.flight.divert