Remove redundant check

The current mission id is set to null in
onIsarStatusUpdate if the robot status is available
before triggering onRobotAvailable, so we don't need
to check if it's null in onRobotAvailable.

backend/api/EventHandlers/MissionEventHandler.cs

@@ -111,21 +111,6 @@ private async void OnRobotAvailable(object? sender, RobotAvailableEventArgs e)
                 return;
             }
 
-            if (robot.CurrentMissionId != null)
-            {
-                var stuckMission = await MissionService.ReadById(robot.CurrentMissionId!, readOnly: true);
-                if (stuckMission == null)
-                {
-                    _logger.LogError("MissionRun with ID: {MissionId} was not found in the database", robot.CurrentMissionId);
-                    return;
-                }
-                if (stuckMission.Status == MissionStatus.Ongoing || stuckMission.Status == MissionStatus.Paused)
-                {
-                    _logger.LogError("Ongoing/paused mission with ID: ${MissionId} is not being run in ISAR", robot.CurrentMissionId);
-                    await MissionService.SetMissionRunToFailed(stuckMission.Id, "Mission failed due to issue with ISAR");
-                }
-            }
-
             _startMissionSemaphore.WaitOne();
             try { await MissionScheduling.StartNextMissionRunIfSystemIsAvailable(robot.Id); }
             catch (MissionRunNotFoundException) { return; }